Disney had no problem killing everyone on Rougue One
shyt they actually green lit a way darker ending than what was originally shot.
My thing with important characters dying is that eventually they will be brought back. There's too much money to be made with movies that have them in their titles. Hawkeye, Widow, Vision, Wanda, etc. can get got and it wouldn't hurt the MCU that bad. But if you are offing Downey or Evans, those characters are too big to not return eventually (with other actors, most likely).
And in that case, it would be interesting to see if the movie going audience would be as
about deaths and resurrection as the comic book readership is