I wouldn't give a shyt quite honestly.
And what set up have they done for Avengers 2? They haven't even finalized the script for the movie.
Every fukking actor who appeared in that film is replaceable.
And what the fukk makes you think they have to hit quota for the next film? Avengers is the third highest grossing film of all time. The sequel isn't likely to top that regardless of who the actors are portraying the characters.
In these types of films actors get replaced. By your logic The Dark Knight should have bombed because Michael Keaton and Jack Nicholson aren't in it.
Then its no longer necessary to cont this debate then friend