Fairly Certain Black Widow has her solo movie, so offing her completely, even if it is a prequal, would be pretty silly on Marvels part.

Those posters are just wonderful though. Now in theory time, Spoiler: so we're already taking a pretty big detour from the original comic, to the point where i don't think anyone actually knows what is going to happen in this 3 hours! Adam Warlock was pretty critical in the comic but is nowhere in sight, and i think it's a pretty safe bet they'll be time travel (so the likes of Loki and Gamora could/will be saved depending how far back they go) and that this will rest on some of the bigger characters being sacrificed to achieve this (i remember there being a plot in the 90's spiderman cartoon where Cap and Red Skull where trapped in limbo for decades, so this might happen to Cap/Iron Man? I'm fairly sure Thor's going to survive seeing how well Ragnarok did (and we need our Thor/Captain Marvel movie directed by Taika Waititi, make it happen Disney!) Hulk i dunno, he still has potential (and we need She-hulk DAMNIT!) but marvel might want to cut mr spoiler lol.