Alrighty, I was supposed to write this all out in gruesome detail to gross out all you people who loved or hated the FMA movie, but I'm lazy, obviously, so I will submit the omake first!
Ed crashed spectacularly into the remains of the old city beneath central, because dammit Jim, he's an alchemist not a pilot!
He somehow finds his way to the array that he blasted through, with Alphonse's help activating it. Unfortunately, Al has suffered a backlash from his blood mixing with red stone liquid and the dying homunculi. Ed walks up to the flesh lumps on the array when suddenly a raw, skinless Al crawls out of the pile, reaching towards Ed. Ed screams bloody murder, transmutes his prosthetic into a blade and stabs the gross looking zombie Al.
Al looks on in disbelief, too drained from powering the array to move. "Brother?" he whispers before falling over dead. Ed finally stops freaking out and sees the red Flamel cross jacket and realizes that after all the crap he and Al went through he had just killed his own brother.
Winry and Scieszka, who had fallen through the ceiling onto something soft enough not to kill them, let out horrified screams as they see Ed kill Al. Then another part of the dome that had sustained residual damage from the battle above causes the roof to collapse upon both of them, causing their untimely deaths. Ed sees the pool of blood seeping from where Al's body and the girls used to be. He screams in pure emo fashion at cruel fate having destroyed his reasons for coming back to Amestris.
But wait! Ed hasn't died… the terrible drama isn't over yet! He shakes off the minimal rubble that ended up on him and flees the scene as if the hounds of hell are after him, which they may very well have been with the gate open.
He comes to the surface only to find that dead baby covered armor were carrying bodies of dead soldiers and State Alchemists past him. Among them was Roy Mustang, whose face and clothes revealed him to have been shot several times by a high-caliber rifle, the back of his head open and spilling brain matter onto the street. Lieutenant Hawkeye, recognizable only by the tag on her uniform, was charred, her uniform pealing back to reveal horrible burn marks.
Ed runs from the grisly scene in horror.
Up ahead, Ed sees Armstrong is mortally wounded. Lying beside him is Fury, who oddly enough seemed to glow around the throat (Ed's guess is that he choked on a rogue sparkle). Without seeing Ed, Armstrong performs his family's special suicide technique handed down through generations. His head promptly explodes into pink sparkles, taking out everybody in a 2-block radius.
Miraculously surviving yet again, Ed wanders dazed throughout the city. He soon enough encounters crazy Nazi lady of whose name we know not. Overcome with grief, he succumbs to her crazy Nazi lady power. He is zombie-fied by dead baby power and helps her go on to exterminate or enslave everyone in the Shambala/FMA dimension. Bringing back conscripted slave warriors and new alchemical-based technology (and dead baby power), crazy Nazi lady helps Hitler and the Nazis take over the entire world.
Shortly after exterminating all non-Aryans, an Aryan-specific flu virus wipes through the remaining human population, and the earth is completely exterminated of human life.
After which ferrets rule the world, for centuries to come. (Except for Australia, who's still like "WTF mate?!?")
PS. FMA fans, flame to your heart's content. I await thee with sword drawn.