In the source material the Marvel Cinematic Universe draws upon theres a much-maligned concept called Comic Book Death. The unfortunate trope carries the truism that any time a character is killed off in a superhero comic, its rarely (if ever) permanent: any major character that kicked the bucket will be resurrected thanks to magic, a universe reset, or some other ridiculous jiggery pokery. Theres yet to be any of that in the MCU so far - unless SPOILERS Bucky counts in The Winter Soldier - but they arguably have something much worse. Its a matter of public record that almost all of the heavy hitters in the Marvel Cinematic Universe have signed, like, ridiculous contracts. Dozen picture deals and the like. Theyre mostly locked in to star in Marvel movies right up through the next decade or so, with the recent announcement of the companys slate of films due out until 2020 all adding to the general issue that theres no real sense of threat. None of these characters are going to die, and audiences know that. Obviously no cinematic hero is ever really in any peril, but itd be nice to at least pay the concept lip service.