Killing off one of the major heroes would be a great instigator for the Superhuman Registration Act in the Marvel Cinematic Universe, because it could potentially make some of that character's fellow heroes say things like "we didn't sign up for this", in which case someone in a position of authority could then give them the opportunity to do so (the government, S.H.I.E.L.D. etc - the latter of whom we'll get to in just a minute). A death seems like the ideal opportunity to give other heroes an official option to, literally, sign up to putting their lives at risk or opt out - especially on top of other factors that would push for superheroes to register.
