My quick theory on how Season 8 will end, pay attention because it's very short. This is a bit of a joke so don't take it too seriously. Parody/fair use.
Aftermath of King's Landing destruction and the Cleansing Crusade
Daenerys takes over the Seven Kingdoms and crowns herself Queen. Tyrion is disgusted with her actions and resigns as Hand of the Queen but is locked up to be dealt with at a later date.
Unsullied and Dothraki remain loyal and act as enforcers with Greyworm captain of the Guard and Hand of the Queen, everyone else defects. Jon Snow formally starts calling himself Aegon Targaryen. His group of rebels start calling themselves "The Exiled Ones" and leave King's Landing to return at a later date when they are stronger.
Dany totally flips when all kingdoms reject her claim to the throne and begins what she calls the Cleansing Crusade. If nobody will accept her rule, then she will burn everything in her path and remake the Seven Kingdoms in her own way from scratch. Over the coming years many towns, villages and keeps will fall to the might of her army and her last living dragon. Sometimes her advancement is postponed by wounding her dragon, but it is only a matter of months, years at best until the Crusade resumes. The true Long Night has come, the sun no longer shines in Westeros, winter will be here to stay for a generation.
Greyworm is tasked with tracking down the Exiled Ones who go into hiding. Over the years they are discovered and each time they have to flee and the recycle repeats. At some point the group will reunite with Sansa, Brienne and Samwell Tarly.
An old crone will come to Aegon and beg him to travel east to the Shadow Lands in Asshai where salvation lies. This is later revealed to be Melisandra reborn who thinks she has failed humanity once before and doesn't want fail again. In Asshai, Aegon will find the weapon needed to end Dany's reign of terror for good: the artifact Dragonbinder. At this point, 20 years have passed and half of Westeros has been destroyed. Attacks have also begun in Essos against the free cities who would dare aiding the refugees in defiance of the Mad Queen.
The Battle of Asshai
Some time later Asshai is attacked by a group of Unsullied and Dothraki intent on killing Aegon who's been discovered yet again. They are defeated but their commander, presumed to be Greyworm at first glance, challenges Aegon to a one on one fight. Aegon accepts.
However once the challenger takes off his Unsullied helmet it is revealed that he is neither Unsullied nor Dothraki, but a Westerosi, a traitor in Aegon's eyes who sided with the Mad Queen against his own people.
"Can you know victory without first knowing defeat? Come! Fail! Die!" the traitor taunts him. Aegon dismisses his ramblings and attacks.
The two duel for 24 hours straight as thousands watch until Aegon, despite being badly wounded, gets the upper hand. The traitor is weakened but he's not done yet, he taunts Aegon a final time saying "You think you've won? You will know the taste of defeat, even if it means my own death! You know nothing, Aegon Targaryen! Nothing but ash will be left where we stand!"
Bran sensing that something is off calls to Aegon "No! You musn't kill him! Stop!"
Too little too late as Aegon is unable to hear him from the sounds of the cheering crowd and finally plunges his blade into the mysterious stranger's chest, sealing his fate. "Dracarys... mother!" Aerys III Targaryen says as he goes down, the adult son of Aegon and Daenerys. A letter from the Mad Queen found in his pouch later confirms his true identity. In her madness, Dany had forced Aegon's hand against their only child.
Aegon is broken inside but stands firm wishing to fulfill the promise made to his people.
"We are going home!"
The Final Confrontation
The Exiles Ones return to Westeros stronger than before and comes across some rebels from the Brotherhood Without Banners in the wilderness near King's Landing who have been fighting Dany's reign for decades at this point. The rebels resent Aegon for leaving, but soon follow him. Using their connections they agree to cause a distraction to get Dany away from the capital long enough for Aegon to secure what remains of the Red Keep. The plan works. With Dany gone, Aegon takes a smaller group to infiltrate the Red Keep. They find an older Tyrion and Ellaria Sand, the only surviving prisoner from Cersei's rule, still alive and the two join the fight. Dany had kept Tyrion alive mentally torturing him, promising to kill him last once his beloved Westeros was completely destroyed. The Unsullied guarding the Red Keep along with Greyworm was killed.
In his dying breath Greyworm confesses to his atrocities, he had become disillusioned with Dany over the years but he never believed Dany could be stopped. Aegon forgives him and he dies at peace, knowing Dany's reign will soon be at an end.
They put Dragonbinder into position atop the Red Keep ready to use against Dany's dragon Drogon. Reading the inscription on the artifact Samwell Tarly makes a shocking discovery that nobody knew about. Whoever uses Dragonbinder will die, his or her lungs turning to coal. Someone will need to make the ultimate sacrifice to stop the Mad Queen.
"At least we've done all we can," Bran says with relief.
People prepare to take cover in case anything goes wrong. Melisandra would do it as she is dying anyway but her body is tainted by too much dark magic for it to work. She knows the honorable Ser Davos would if he were here but he died years ago. The soldiers are trying to decide on who should sacrifice himself, but a single brave young man steps forward to blow the Dragonbinder. Aegon pushes him out of the way.
"My king? But..."
"Every choice, every sacrifice has lead me to this moment... to face her!" Aegon says.
"You... you're not coming with us?" a tearful Samwell Tarly asks.
"Jon? What are you doing?" Bran asks, one of the few people close to Aegon that are still allowed to use his old name.
"The Iron Throne is nothing without a ruler. Did you not see this fate, prophet?" he says with a bittersweet smile.
"Our freedom was never in fate's hands..." Bran replies "Farewell, Jon Snow. Now you know everything."
Aegon hugs his family and friends one last time before facing Daenerys.
"Dracarys!" she says ready to burn Aegon to death. Too late.
"Auntie, your crusade... is over!" he taunts her blowing the Dragonbinder and sealing both their fate.
"No!" she says as she is knocked off Drogon. The dragon now loyal to Aegon destroys what remains of the Dothraki and Unsullied forces who were preparing to storm the Red Keep and help their queen. A wounded Dany limps over to her throne. Arya comes out cover to deliver the killing blow.
"You're the last on my list you know, you have been for a long time, as my friend once said, I've been chasing vengeance all my life," she says.
Dany doesn't say anything but Arya sees the anger and resentment in her green eyes.
"No," a dying Aegon says, "the one who passes judgement should swing the sword..."
If this was anyone else she might have protested being denied yet another kill, in the end she figured everyone had their own little lists... and this was definitely even more personal. Arya decided to leave Dany alone with Aegon in their final moments.
"We could have been so much more than just subject and Queen, Jon... Traitor..."
"My name... is Aegon Targeryan... and you are not my Queen. You've never been a Queen."
Dany sheds a tear hearing him say that.
"Promise me no harm will come to Drogon," she pleads with Aegon knowing death is near.
"You know I'm an honest man, so you must know that's not going to happen. You lost your right to make demands when you sent your own son, our son, to die by my hands."
"Was it all for nothing, Jon?" Dany asked, tears running down her cheeks...
"No, the wheel will be broken, Dany" and with that he delivered the killing blow.
Conclusion
After killing Dany he collapsed on the floor next to Dany's body, shorter of breath with each passing moment. Drogon flew over to check up on him. Soldiers and archers gathered around Drogon. With his last breath he said only one word before finally succumbing to the deadly effects of the Dragonbinder: "Dracarys!"
The dragon then melted the Iron Throne and reduced both Dany and Aegon's bodies to ash, her dead body no longer immune to fire as it had been in life. Their ashes scattered almost immediately upon the winds, making their way to the Narrow Sea. Drogon, still loyal to Aegon's side thanks to the powerful enchantments of the Dragonbinder, did not resist when the soldiers put him down, his body destroyed to ensure no possibility that dragons, living or otherwise, would ever fly in Westeros.
In the aftermath Bran, Tyrion, Sansa and many other survivors formed a transitional council and abolished the monarchy.
The Republic of Westeros emerged out of the smoldering ruins of the Seven Kingdoms and due to the seismic shifts in power the Iron Bank filed for bankruptcy later that year.
Though the game of thrones was over, in time a new war would start between the free cities of Essos and the Republic of Westeros over a newly discovered resource in the far east Shadow Lands following Aegon and his people's exodus: the Assharite. War never changes.