at this point the only 2 that could really die with any impact are Cap and Tony. they can't just retire. I don't know shyt about the comics, but here's my quick 2 second, no thought whatsoever ways to "keep those characters alive" going forward.
Bucky and Sam are backed down into a corner, and about to be offed. Steve has a huge heroic moment where he somehow sacrifices his life for both of them. They do a "Captain(s) America" movie where Sam and Bucky share the mantle.
Tony has the big death in the climactic battle. We find out that he somehow learned how to transfer his consciousness into A.I. and he becomes the new Jarvis going forward. He is the voice of whoever wears the armor beyond, and for Spiderman, maybe even appears every now and then as a hologram. RDJ gets to remain in the MCU without working much, and still collects the checks he'd probably be collecting regardless
oh and Loki dies for good. depending on how it's done, that would be impactful. I can see Drax dying too, and getting a Gladiator style shot of him entering the afterlife to meet his family.