Coulson is the first, but not the last. After all, with a profession such as theirs, it’s only a matter of time until the final blow. Nobody becomes a spy or joins a league of superheroes with the intention of making it all the way to their pension. Well, maybe Coulson did, but look where that got him. Stabbed through the back by a vengeful demi-god. At least it was quicker than some other possible deaths. At least it serves a purpose, you could also say, it brings them together, makes them fight harder and win. This time.
Bruce is the next one to go. No one would have expected it, especially after his confession about the suicide attempt, but there you go. Bruce is second. He’s on the sidelines for this one, they’re trying to avoid too much destruction if they can help it, and Bruce is with the SHIELD agents at the periphery when the bullet finds him. It comes from behind him, a sniper hit, that’s why he doesn’t know it until it’s too late. The bullet shatters his spine and buries itself into his heart. Too fast and too deadly even for the Big Guy. There’s nothing much anyone can do. Bruce is dead before any of his team makes it back.
Natasha wakes with a start one night and finds herself holding the hilt of her knife buried deep in Clint’s neck. Clint’s eyes are wide, awake and aware of what’s happening before her brain even makes the connection. It’s only been a matter of time for the two of them, and she doesn’t apologise. He just looks at her and there is no accusation, no anger or sadness, just calm acceptance. She knows what she has to do. She pulls out the knife and uses it to cut her own wrists. The second one is harder, her hand almost useless from the deep wound pulsing blood, but she manages. They find them like that the next morning, blood soaked into the mattress so deep they have to burn it. They burn the bodies too and the stones on the wall only carry their names and nothing else.
Thor makes the trip to Asgard one day and simply doesn’t return. There’s a summer full of storms and forest fires and temperatures playing haywire. Scientists say it’s because of global warming, but no one is quite sure if that’s correct. Eventually Jane Foster gets the Einstein-Rosen-Bridge to work and when a carefully selected SHIELD team sets foot into Asgard, all they find is a world full of burned out ruins, darkened skies and bleached bones. Ragnarök, Erik Selvig mutters and looks sadly at the destruction around them. They find Thor’s bones in what appears to have been the central hall, roughly nine paces away from the skeletal remains of a huge snake. They turn around without touching anything, there’s nothing to be gained in this dead world.
Anthony Edward Stark
Tony drinks himself to death. It starts with Coulson, or maybe it started long before that, but he’s careful about it and manages to hide it for a long time. After Bruce it gets worse and once Clint and Natasha are gone he’s not even hiding it any more. Pepper and Steve find him one morning, on the highest accessible point of the Avengers Tower. There’s an empty bottle of single malt in his left hand and his arc reactor in his right. He’s smiling, staring out into the night with unseeing eyes. Pepper doesn’t cry, not in front of Steve. She bends down and closes Tony’s eyes, says that he always felt like he was living on borrowed time and maybe, Steve thinks, maybe it was good that Tony got to choose his own death.
Captain America/Steve Rogers
Steve is the last one. He keeps dodging the proverbial bullet even after all the others are gone and buried and on their way to being either forgotten or glorified. But in the end, they get to him too. He dies in a roar of flames and what the ice failed to do, the fire does with a vengeance. When they finally manage to douse the flames, there’s nothing much left to find. A few teeth and bone fragments, brittle and blacked from the heat. They resurrect the monument at Arlington and that’s the last of the famous Avengers gone.