Even after Thanos killed off half the main characters I knew that the likelihood of any of them miraculously reappearing in later outings had more to do with the actors’ contract negotiations and desire, or lack thereof, to do any more Marvel than it did with any plausible plot device that could resurrect them. The end of the world didn’t even matter in the viewer’s mind because everything in the Marvel “universe” is so arbitrary and can therefore be completely changed on a whim.
I should add one more thing: I think the reason Iron Man was so much more popular than other characters is that his character is the most reality-based, and therefore most relatable and believable. Not that Disney might not still invent some magical way to bring him back, but in the original storyline at least there was some real dramatic tension because he was mortal and could die. Not so with the menagerie of more fantasy-based characters. Of course, this isn’t entirely Disney’s fault; it’s a weakness of the source material. Comic books just don’t make very good movies. One exception was the Christopher Nolan Batman movies, and they were great because Batman, like Iron Man, has no fantastical powers, and because Nolan wisely made his movies even more grounded in plausible reality than than that.