This is a scenario or more like a sort of a different story set off to a different way like an event that has changed its course, this will take place in Warcraft about what would really happen if Kael'Thas didn't side with the Naga and somehow sided with Sylvanas on a rebellion over Lordaeron to reclaim it against the Undead Scourge, by siding with Sylvanas he was able to survive the onslaught of Undead forces and with her help and her partner Varimathras by her side they could defeat the leaders of the Scourge to reclaim the capital city.
It begins when Kael'Thas and his Blood elves were attacked by the Undead by the western coast while the Alliance were defending the Capital city from another Undead army, right now he has lost all his bases on the mainlands and the only one left is his main one that remains on the island but still attacked by the undead flyers, if he can't hold them off he would have no choice but to abandon the island and retreat back to the Capital city to make a final stand there, but the problem is that even if he does retreat he would disobey Lord Garithos orders so he must go on the offensive against the Undead or losing this whole sector to them.
Kael was stuck out there for a while now, this day will probably take on the events on when the blood elves and naga face the night elves in Outland but now it's changed and he is still fighting the Undead. Kael has manage to destroy two undead bases from the north and south but attacking the other two short bases will be difficult as the true Undead bastion is defending their positions to retake back the areas, Kael stands on the south, seeing more undead forces marching over the bridge to send them back to the island but Kael would destroy the bridge and cause them to retreat back, attacking the south western base will be a problem when he needs to attack it by the sea so he ordered his forces to evacuate the south base and head to the northern base to try and strike the Undead there while the base on the island is holding off against any air units as they come from the western undead base. Kael and his forces were too late as the elves that were defending that area were killed and was forced to return to the island for a strong defence but he knows that he cannot win this fight so he ordered a retreat back to the ruins and back to the capital city where Garithos and the Alliance is, he will take the responsibility for failing the mission as the Undead would start to cover this whole area in the blight.
Kael and his forces marches to the city where Garithos is ready to defend against the forces of the Dreadlord named Detheroc as he is preparing a force to the south but hasn't attacked yet, Garithos would prepare a strike force to attack the base but spotted Kael'Thas and his elves returning from the attack.
Garithos would ride towards Kael as he looks angry since he knows that he retreated from the undead scourge and left the western front wide open for an attack by the Undead. "Kael!" he yelled at him as he rides towards him. "I thought i told you to defend that area with your lives! But instead you fled and left the whole area to Undead. You blood elves are weak, no wonder your city was taken over so quickly."
Kael would try to ignore what Garithos said about his homeland, he simply looks to the side then back to Garithos "I did my best to hold them off, but we couldn't defe-"
Garithos "I don't care!" he interrupts him "Right now we were preparing a strike to the Undead, but since you fled we would have to cancel that attack. However if you wish to serve the Alliance then you send your elves outside of the city to attack the Undead forces while we clean up your damn mess."
Kael "But milord we can't go out there now, my people needs to re-"
Garithos interrupts him again "I don't care how you elves do it... just get it done!" he would ride back to his base, along with his soldiers to prepare a defence instead of an offense.
Kael would soon order his elves to head to the north to establish a base there so the humans can defend the western side of the city before the undead arrive to siege the west; this will cause the Dreadlord named Detheroc and his undead force to attack from the north, strong flanking positions against the city of the Alliance. While there defending Kael would defend the north hills against any undead force that will come and when they come they will strike down the Blood elves hard and this time Garithos will not let the blood elves inside his city if they fail to hold them off.
Today this will take the events of when Arthas starts to lose his energy and forces a civil war between Sylvanas and the Dreadlords that controls some parts of the cities of Lordaeron, and because of that it won't be long before Detheroc prepares an attack on Kael'Thas and another attack from the west. Detheroc would try to control the humans inside the city but he needs to get into position so he would have to take out the blood elves if he wishes to control the city and Garithos. Varimathras would be battling against Sylvanas and her followers while Detheroc prepares an attack on Kael and his elves as they cannot lose that reach against the Dreadlord.
The blood elves prepared a defence as the undead are coming, he would set off some magical traps to hold them off for his archers to get into perfect positions to shoot down at the undead infantry as they get close to the roads to the city, Detheroc himself will join the fight as he sends demons and undead to strike the Blood elves while the undead from the west sieges the gate and tries to storm in but Garithos retaliates and pushes the undead back outside of the city. Everything was going so well but then the demons interrupts the blood elves and strikes through the cliffs and the roads from east and west. Kael tries to get those areas under their control but they couldn't hold against the demons as they prepare to march past the elves and towards the front gate, due to the breakthrough they cutted the blood elf forces in half, killing all the elves from the west and by losing nearly all his forces he would have to cut through the east to get an escape as he couldn't hold them off anymore but Detheroc entered his base and slaughtered the elves before they would escape, most of them did but Kael got attacked by Detheroc and got captured. Since his mind control wouldn't work on Kael he decided to lock him up and make him slowly die inside while his elves flee from the sight, once they were gone the Undead storm the front gate and attack the city while Detheroc tries to control half of the armies of Garithos inside the city so that he can use them as pawns if anyone out there tries to retake the city.
Sylvanas has defeated Varimathras and has taken control of his forces, she would hear the rumours from him that there are blood elves out there trying to get Kael out of the dungeons, if he is still alive she will go solo on this and save Kael herself as he could be a perfect ally against the forces of Detheroc and Garithos. Kael'Thas is now stuck in a magical prison so his magic can't get him out; some of the elves that tried to get him out got themselves captured by the humans while Detheroc sends his undead hordes through the city to control half of it while Garithos controls the other half. Kael would start to give up as he lost everything and failed his kind that he couldn't defeat the undead, as all hope was lost Sylvanas came out of now where and killed the prison guards and released him out of his prison cell.
Kael would look as a shock as he sees Sylvanas an undead "Sylvanas? Is that you?" He notices she's an undead like the others "Your... dead..." Sylvanas simply shakes her head as she places her bow on her back.
"No Kael. I am this monstrosity instead. I have come to save you from this place and wish for you to side with me on attacking the Scourge together." She turns back "Your elves are here also, we should find them before they die in here."
Kael would take a step forward "Wait... Sylvanas... i don't understand, how I can trust you when you're a..."
Sylvanas "I know Kael... right now we are going to take back Lordaeron from the Dreadlords controls, i need your help Prince Kael."
Kael thinks for a while then he would nod "Ok... it's Kael now, i am no prince anymore." He would follow her to save the other blood elves that are imprisoned here.
After a while of fighting them finally got out there and joined forces with Sylvanas, it was hard to coop with them since she controls the undead and a Dreadlord by her side but Kael would trust her as she could be telling the truth about this whole rebellion while Arthas is elsewhere away from his kingdom. The elves form together with the forces of Varimathras and Sylvanas in the north, preparing themselves to attack the city while both Garithos and Detheroc are asleep within, before they would attack Kael would stand on the edge of the cliff, seeing the battlefield of where he defended a week ago, still seeing his dead elves as he thinks he lead them to their deaths. Sylvanas would walk over to Kael as she too saw them died when she was here before she would go after Kael.
Sylvanas stands next to him "I am sorry Kael. We must defeat the undead here for Quel'Thalas."
Kael "Whats gonna happen once we take over the city. You still going to command those things back there?" he looks back seeing Varimathras.
Sylvanas "There is an old saying... the enemy of my enemy is my friend." She whispers that last thing she said and joins the others to march to the city to reclaim it from Garithos and Detheroc. She orders her forces to attack the front gate while Kael goes to the side with all he has to siege the west to attack Garithos and his men while she and Varimathras battles the undead and Detheroc, they would not leave anyone alive but after the undead were no more Kael decided to kill off Garithos and command the humans once this is done. Varimathras didn't like this but Sylvanas accepted this and made Kael command the humans, ordering them to leave the city to join them to the capital city to fight the last Dreadlord, Balthazar.
A week has passed and they are finally prepared to attack the capital city as it's well defended since he knows that Sylvanas, Varimathras, Kael and the humans are preparing to march to the city to take over it, with Kael attacking from the south east with his elves and humans and Sylvanas and Varimathras from the north west with the undead, they would all charge to Balthazar in hope that this is enough to siege the city and kill Balthazar, with him dead then the rest of the undead will serve Sylvanas under her banner to create the Forsaken. Before they would prepare an attack Kael wishes to speak to Sylvanas alone before they would attack Balthazar.
Sylvanas looks curious at Kael as something was wrong as he came to speak to her alone "Is there something wrong Kael. Can't this wait after we defeat the Scourge?"
Kael would look over to Sylvanas "Sylvanas, once this is over... the humans and us blood elves will not be a part of your force anymore, you know this."
Sylvanas "Hmmnn... i understand what you are saying Kael. You blood elves have been hunted by the dead and now were siding together."
Kael "Once this is over... me and the others will return back to the city, i will try not to let them attack you or your allies but know this. Once we have recovered when we return to the city, we will reclaim Quel'Thalas from the Undead, with or without your help." He would start to return back to his base while Sylvanas thinks for a while before returning to hers.
The final battle for the capital city has begun, Balthazar was ready and prepared the demons and undead forces in the area to attack these two bases to stop them from attacking his main base in the middle of the city but they continued to attack the main city and ignored the other bases in the area. They would take alot of attacks from their bases if they ignore the other undead bases in the area but they would lose alot of resources if they attack all bases in this whole area of the capital city so they have to risk it and charge to kill Balthazar and hope that the undead forces will stand down and serve the Dark lady. Prince Kael'Thas and his forces broke through the lines and manage to get inside to destroy some of the bases while Sylvanas forces were struggling to hold off Balthazar and his demon forces as he ordered his demon horde to attack her first before attacking the elves and humans, with Kael's help he destroyed the dimensional gate to stop any more demons from attacking, breaking Balthazar's forces but it didn't stop him from slaughtering alot of their numbers but they still continued to attack as Kael found some dwarves from the north, joined in the fight and destroyed some of his buildings.
Sylvanas finally rushed into the middle of the city with Varimathras and her undead forces to help out Kael; with them together they would cut a deep blow within the Undead Scourge as they will soon to win this fight once and for all, after all they have been fighting for only a few days now but finally they destroyed the middle base and captured Balthazar and causes the other undead bases to stop and surrender to the dark lady.
The three would be together before Varimathras would kill Balthazar; Kael did start to act suspicious with Varimathras as something doesn't feel right as he killed Balthazar in front of him. Kael would look at Sylvanas after Balthazar lies dead on the ground. "Sylvanas, it's time for me and my forces to return."
Sylvanas simply nods "Farewell... Prince Kael'Thas. One day i will help you reclaim our homeland, but that day hasn't come here yet." Kael simply nods and then returns to his forces, ordering them to retreat back to the city they were in before so they can recover and regain their strength so that they can maybe attack Quel'Thalas.
Varimathras looks at Sylvanas "It appears you still have love for your elves in you milady, or is it because you started to feel love for-"she interrupts his sentence.
"You don't want to finish that sentence of your Varimathras... Let's go." She would return to the capital city to gain control of the other undead forces in the area.
For a long time has passed both sides stayed neutral to one another but not a full grown alliance. Sylvanas finally got control of nearly all of the undead forces, renaming the Scourge the Forsaken and claiming the throne as the banshee queen. Over a while now the humans still stays with the blood elves but they slowly disperse from them as they still wish to reclaim their home too and so they became the Scarlet Crusaders, finding more humans out there to fight against the Forsaken while Kael still remains in Lordaeron with all his elves, preparing to march to Quel'Thalas in hope to make a final attack against the last of the Scourge in this land but not alone as Sylvanas herself shall join alongside with him in hoping to take over Quel'Thalas and maybe reclaiming the throne of king in the city of Silvermoon for the glory of the Blood elves.