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One by one their seats were emptied.
One by one they went away.
Now the family is parted.
Will it be complete one day?
Thor was the last to go. If he ever truly died, that is; death has different rules in different dimensions. It was more like he just ceased to exist any longer. The legends of the Norse gods grew less frequent, appeared in fewer story books and legends, and eventually were completely forgotten. And with them, so was Thor.
Banner outlived the human Avengers, although the Hulk still survived. The times when he was actually Banner were sporadic towards the end, and at some point he gave up; no one knew exactly when. The Hulk could only confirm that Banner was no longer sharing his conscious.
Tony lived long enough to almost completely become a machine. He was on life support for nearly a month before the rest of his organs crashed like a freeway pile-up. Even the arc reactor could not prevent cancer.
Steve died long before Tony. The super serum was all but useless when trapped under water. A crew recovered his body and did everything they could to restart his heart; hell he still felt warm. But after four hours of defibrillation and chest compressions he was declared dead.
Natasha caught a bullet in her femoral artery that caused her to bleed out. The blood loss made her too weak to fight back and keep the villain from snapping her neck.
Clint died three days later. He put a bullet through his chin that ripped a hole through the top of his skull in his apartment. They buried Natasha that morning.