I think they might kill Captain America :( sorry for all the Captain Amercia fans our there, I am one too but technicly, they can't kill Thor because he's a "god", they can't kill Hulk because the hulk won't let him (he's tried to kill himself already), and they can't kill Iron Man because Robert Downey Jr. signed on to do 2 or 3 more Iron Man movies. As to Black Widow and Hawkeye, I don't think they had as big a role in the Avengers as the others.