re: Researching Avengers 4 - Spoilers

You can make a lot of good guesses on this just by knowing how well certain movies have done in the box office and what sort of time those actors/tresses have left on their contracts.

For instance, although the Captain America movies have done extremely well (and seemed to get better as they went on, at least to me), Evans has said he wants to concentrate on working from the other side of the camera. If I remember correctly his contract with Marvel (to play Cap) is up after A4 so most likely he will be passing along the mantle after that movie (to either Bucky or Falcon).

Spiderman: Homecoming seemed to breathe new life back into the franchise, but there's no telling how long that will last since they screwed it a bit by SJW'ing his friends into a mini-UN and made Aunt May a hottie.

T'Challa is going nowhere. Period. He's currently the Green Panther

Hemsworth is interested in doing at least one more Thor after A4 so you can expect the god of Thunder to continue surviving.

Ruffalo still has 2 movies left on his Marvel deal. Although there's no word yet on another Hulk movie, it does mean he would have at least one more left after A4 to HULK SMASH all over the place.

ScarJo will be in A4 and there's a solo movie that's been in the works for a while. She's talked about her contract with Marvel having changed over the years so the Widow will probably live on.

Renner should have 2 movies left in him after A4 (contracts generally were for a 6-movie deal, A4 would be his 4th). There is talk of a Hawkeye solo movie option, but nothing being worked on that I know of.

Cheadle and Mackie each have more movies left on their contracts (3 each, I think). Expect them back, if for nothing else than to take over the roles of Iron Man and Cap from Downey and Evans.

Olsen's character will be back in A4 considering the Scarlet Witch has appeared in only 3 of the 6 contracted movies (cameos don't count, btw). She has a TV show in the works so her time in later movies could be limited.

Bettany has appeared in 8 Marvel movies if you count him as the voice of J.A.R.V.I.S. It's been documented he's in A4 (probably as Vision) but no word on what his current contract contains. He could be totally solid for at least another movie or two, or he could just fade through the background...

Rudd has described his Marvel movie deal as "three-plus-plus" so he has at least 2 more movies worth of growth (or shrinkage *cue George Costanza*) left so he will definitely be back as Ant Man.

The Wasp's newest costume has shown up in a PSA somewhere so we don't have to Hope that Evangaline Lily will be back as the Wasp in/after A4.

It's likely Cumberbatch signed a multi-movie deal. It's not outside the realm of possibility his deal was for fewer than the standard 6, but it would be... Strange for him to not come back with and after A4.

Larson's character hasn't even hit the screen yet. If she's getting the same 6-movie deal then it's a safe bet that even if Captain Marvel tanks she'll be a central figure in marvelous Avengers movies beyond A4.

As for the GoTG crowd: They original cast has been contracted for at least 3 GoTG movies but with their refusal to move on the 3rd movie without Gunn, there's no telling what will happen there. At the very least we can probably bet on having Rocket and Groot return (since they are CGI, the only issue would be finding voice actors close enough to the originals).