To say Avengers: Infinity War set a rather solemn tone for the otherwise upbeat Marvel Cinematic Universe is a massive understatement. For many viewers, especially those who were unfamiliar with the Jim Starlin, George Perez and Ron Lim miniseries The Infinity Gauntlet (and the adjacent lead-ins and follow-ups), seeing half of the characters we've they grew to love over the last decade turn to ash at the literal snap of someone's fingers was devastating.
Now, anyone who applies one iota of critical thinking to the situation or is even remotely well-versed in comic book storytelling knows death is nothing more than stasis for superheroes and that the costumed heroes who vanished will be back (lots of sequels in the works, guys). The real question is how those who were not affected by Thanos' plan will fare in the sequel.
There has been plenty of speculation regarding whether or not actors like Chris Evans, Robert Downey Jr. and Chris Hemsworth will hang up their proverbial capes (or literal cape in Thor's case) after the forthcoming Avengers: Endgame. This speculation is by no means unwarranted.
The aforementioned actors have been part of the MCU since its first phase and each of them have had their own trilogy of solo films to tell their stories. If any, or all of them, were to step down from their already iconic roles to peruse other avenues, it would be understandable. Well, there might be some mild rioting on the internet right after, but people would get over it eventually.
Oddly enough, because of the final moments of Avengers: Infinity War, in which half of all life is snapped out of existence, the stakes for Avengers: Endgame seem so much more dire. Those who are left behind are at risk, as their once beefy ranks have been significantly whittled down. We, as an audience, have witnessed the worst case scenario play out on the screen for our heroes, and if another sacrifice has to be made to fix the world (nay, the universe), some long-standing characters might be on the chopping block.
Yes, we would love for Avengers: Endgame to be comprised of just scenes of Thor and Rocket dunking on Thanos for three hours, but if the film turns out to truly be the turning point for the franchise, we may be saying goodbye to some beloved heroes.
For a film to have emotional weight or to be a cathartic experience doesn't necessarily hinge on finality or the death of a lead character, but those things don't hurt. As far as happy ending go, just putting the world back how it once was would be sufficient... predictable, but sufficient. It would pave the way for the already-in-production films starring previously "snapped" heroes and be a moment to rejoice (we can practically hear the Alan Silvestri score now).
The road to getting there, however, won't be an easy one to travel. If the trailer for Avengers: Endgame is any indication, we're going to walk into a whole heap of sadness and unrest for the first act, or at least until Scott Lang shows up to cheer everyone up with his charming smile and bad jokes (Paul Rudd can do no wrong, you guys). But at the end of the film, we're certain things will be better on a macro level.