There it is in writing in the official synopsis that Disney has released. Their goal is to undo Thanos' actions, which will result in the resurrection of the "dead" heroes since their death will never have happened. If Disney has released this information as part of the synopsis, I'm not sure how it can be considered a spoiler to talk about the existence of future sequels for Spider-Man and Doctor Strange and Black Panther and so on. The path forward for Endgame is clear. The suspense is in how they will accomplish this goal.
Well, just because Disney says the Avengers will assemble to undo Thanos' actions (of COURSE they will), that doesn't necessarily mean they'll be successful in doing so.