Nobody stays dead for long in comic lore.
If you haven't seen Avengers: Infinity War, stop reading now.
For everyone else... what an ending, right? Marvel shocked fans by doing something they have never done before... introducing a villain that actually won. In fact, in most films, comic book based or not, the villain is usually defeated by the end of the movie. It is rare that the bad guy actually achieves his goal, but Thanos pulled it off and collected every Infinity Stone and snapped his fingers. The "snap" killed off half of the universe, including some of our favorite characters.
Now, anyone who was emotionally distraught at the end of the film should take a deep breath. In the comic book world, no one stays dead for long. Nobody. The same will prove true in the comic movie world. Although characters like Black Panther and Spider-Man turned to ashes right before our eyes, we already know that Tom Holland (Spider-Man) begins filming a sequel to Homecoming this Summer, and a Black Panther 2 is already in the works. That means that somehow, the heroes will be resurrected. One cool possibility is the "Theory of the Six," which focuses on how none of the original Avengers perished and they will somehow manipulate time. Set photos of the original six in their costumes from the battle of New York in the first Avengers film seem to back up this theory. Another theory revolves around Ant-Man, who can enter the Quantum Realm, a place where he shrinks so small that both time and space become irrelevant.
Although several fan theories will ultimately be shot down when Avengers 4 hits theaters next year, one thing is for certain. Several characters, even ones that died, are set to star in the next film. Check out this video put together by Looper, that features every hero that has been confirmed for Avengers 4, and join the multitude of fans who are creating their own theories of how these heroes will be used in the film.