Captain America Dies, Bucky Takes The Mantle
One, Steves's death is used as the emotional cliffhanger for Infinity War, with Bucky (Sebastion Stan) and his assumption of the Cap mantle being the hook for it's sequel and Evans' final appearance being a flashback or apparition.
Two, Steve goes all out in the sequel resulting in his death and the Bucky transition is the crux of the next standalone Captain America movie.
Or Three, Neither of these things happen and Evans renegotiates his contract to appear as 'Steve Rogers; Super Soldier' in an advisory role because nobody ever stays dead in comics, everything is a lie, don't believe his lies
Either way, Evens' tenure as the all-American hero is almost certainly in it's 11th hour and given that there hasn't been much consequential death of late in the MCU, Cap going out like a true hero is the emotional gut-punch the franchise needs.
Vision Will Spend MOST of the Movies Dead
So there's far more room for Vision to temporarily die only to be returned to life either via the Gauntlet itself, alien tech, a new version of the arc reactor or by everyone's favourite movie bullshit: the power of friendship/love, delete as appropriate. I understand the argument that he won't have too much to do plot-wise past Infinity War, but his narrative potential isn't over yet. Even if we have him around just as an emotional crutch for a powerful Scarlet Witch breakdown scene, I would say that would be enough to keep him alive for. Or, y'know, Bettany could actually want to go back to being a voice-over which is fine too, I guess.
The Avengers Roster Will Be Very Different
The classic roster of Captain America, Iron Man, Thor, Hulk, Hawkeye and Black Widow are likely to be replaced or retired following the events of Infinity War. My prediction for a 'New Avengers' style team would have Hulk, Spider-Man, Captain Marvel, Doctor Strange, Black Panther, Ant-Man/Giant-Man and Wasp, with the possibility of Hawkeye becoming Ronin and Bucky immediately becoming Captain America. That does leave War Machine, Scarlet Witch and Vision on the sidelines, but they can still be affiliated with the main team without necessarily being on the roster.
Thanos WON'T Die
Thanos is the culmination of almost 10 years of storytelling, so obviously he won't die in Infinity War. I'd put solid money on him being the villain for Avengers 4 as well, but where do you go from there? Well, I think there's a perfect way out of this situation. There is a way to essentially 'kill' Thanos without ever ruling him out from returning: Lock him in an alternate dimension. Whether that's the Cancerverse from the Annihilation story-line or the Negative Zone (Maybe Prison 42?), the Marvel canon has plenty of alternate realities that Thanos can be banished to in order to keep him on ice in the event that Marvel can't escalate the cosmic threat (Read as: In the event that Fox don't do the logical thing and allow Marvel to play with the Fantastic Four property again).
Besides, Josh Brolin probably has more than just 3 movies on his slate. Even if he is Cable as well.
There WILL Be A Future VIllain Set-Up
Question is, who is big enough to step into the big, empty Thanos boots? Well, you could have:
- The Beyonder
- The High Evolutionary
Or my personal pick: Thane, the son of Thanos.
It's the perfect concept! Introduce Thane as a tween kid at the end of Avengers 4, who just watched his father and all his friends get punched into a dying dimension by an army of colourful characters from some backwater planet called Earth. With these new faces making up the next roster of Avengers, Than knows EXACTLY who he's dealing with and who he's out to kill, have him recruit or join forces with anyone from the list above (My personal pick would be him striking a deal with Annihilus to give him control of the universe in exchange for returning his father from the Cancerverse. Marvel, hit me up yeah?) and you have the perfect blood-soaked revenge fantasy story that could lead to hard-hitting emotional moments that can put the entire multiverse into jeopardy.
We just need Marvel to read and use ideas from fan fiction now and I should be 100% on the money.