The only death and resurrection that would make sense in MCU is Thor, he could die during Ragnarok, then fight his way through Hel and come back to the living, and it won't feel out of place. With Cap or anyone else it would feel kind of cheap to die and come back later, but I guess they could always use one of the infinity stones to resurrect him or something.
If Steve does die in CW, someone will only take his place until he's resurrected, Steve will still be Cap for the Thanos fight. (unless Chris Evans really doesn't want to come back, but that's a whole other thing.)
And remember, Avengers doesn't need to assemble unless there is a real reason to do so. Steve maybe dies in CW, Thor probably dies in Ragnarok, Iron man is viewed as a villain after CW.. the Avengers dissembles after CW. Then you get a whole bunch of solo movies where Avengers no longer exist. Then when Thanos is about to show up, there's a reason for the Avengers to assemble again, and this time with new powerhouse like Captain Marvel and Dr. Strange etc. Thor fights his way through Hel and is back, they use one of the stones to resurrect Steve so he's back, and Tony sort of redeem himself along the way, so the old band is back together with new members and meet up with the GotG to fight Thanos.
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