Spoilers ahead for Avengers: Infinity War. Even though Infinity War was almost hyped up to Peter Quill-levels of self-aggrandizement, it still managed to shock everything with its ending. After Thanos achieved his goal of collecting every Infinity Stone, he snapped his fingers and destroyed half of Earth. In the end, we see Thanos sitting on a hillside over looking a sunset — much like Killmonger at the end of Black Panther. But does that mean that also like Kilmonger, Thanos is dying at the end of Infinity War?
Captain America delivered a few destructive blows to the Big Bad before the finger snap, and they may have injured Thanos enough that Infinity War's triumphant villain may end up dying. Thanos won't die, though, or if he does die, he will definitely come back to life since the end of Infinity War left the note, "Thanos will return."
The thing is that death doesn't really mean much after Infinity War, because Bucky, Black Panther, Groot, Scarlet Witch, Falcon, Mantis, Drax, Star-Lord, Doctor Strange, Spider Man, Maria Hill and Nick Fury all vaporized after Thanos snapped his finger. Considering that a Spider-Man movie is planned for 2019 and a third Guardians of the Galaxy installment is confirmed for 2020, you can at least bet that Spider Man, Mantis, Drax, Groot, and Star-Lord will come back to life eventually. Perhaps Thanos even will also die and then come back to life in Avengers 4. Plus, Black Panther has to come back to life. As does Bucky, and Falcon, and... OK, everyone who died in Infinity War needs to come back to life.
So now that we know that death isn't exactly a finite state after Infinity War, does it even matter if Thanos is dying? It could, considering that Thanos will definitely come back. Avengers 4 could end up with the survivors from Infinity War finding him on the hill he — literally — went to die on and getting the Time Stone from him once he is in a weakened state. You can't really know if the Time Stone even exists anymore, since the Infinity Gauntlet (Thanos' metal glove that held the stones) looks wiped out after Thanos snapped his finger.
The Marvel comics don't offer a lot of helpful insight into Thanos' fate following the bloodbath of Infinity War either. The comic upon which the latest Avengers movie is based was called Infinity Gauntlet, Slate reports. In that comic, the Thanos vs. Avengers crossover drama results in Thanos joining the Avengers to defeat Nebula after she gets ahold of the Infinity Gauntlet. Once that battle ends, Thanos goes off to a different planet to live a quiet life as a farmer. Considering that Thanos might have killed half of the Avengers and most of the Guardians in Infinity War — not to mention Loki, Heimdall, Gamora, and Vision, who Thanos killed even before using the Infinity Gauntlet to snap the world's population in half — nobody wants to see him become a hero.
Since you probably can't expect to see Thanos join forces with Iron Man, Thor, Captain America, Black Widow, Hulk, War Machine, Okoye, Nebula, and Rocket — seriously, would you want to? — the best bet for the Avengers' saving rests in all of the time travel theories. Thanos might have even given us a sneak peak of that at the end of Infinity War when he let Scarlet Witch kill Vision, then proceeded to turn back time to kill Vision himself by ripping the Mind Stone from Vision's head. It was a shocking moment, but it also proved that the Time Stone can allow for that kind of thing and Doctor Strange used the stone to look forward in time to find out how the Avengers could actually defeat Thanos.
Considering that Doctor Strange told Tony Stark that giving Thanos the Time Stone was "the only way," you might want to hold off on mourning all of your favorites' deaths. This could all be a part of a larger plan, and it will probably be one involving Captain Marvel since Nick Fury paged her — yes on a beeper — before he disappeared into thin air along with half of Earth's population.