Will Thanos die in Avengers 4?
I think that since Thanos accomplished his goal in the film, he will now attempt to use the Gauntlet's power to fulfill his next desire: reconciling with both of his daughters, and that will be his undoing. I think he will bring Gamora back and try to win her love by using the Gauntlet. Meanwhile, the other heroes will contact cosmic entities to battle him. Nebula will become the new villain when she takes the Gauntlet for herself. Since this Thanos does not desire power for its own sake, Nebula craves it since she has been helpless her whole life and the Gauntlet will supply her with what she thinks she needs. It will be Nebula who will battle the cosmic entities and attempt to rule the universe with the Gauntlet, while Thanos mocks her attempts at using it, and will have to work with Earth's heroes to stop her.
The story will end with the Gauntlet destroyed, and everyone thinking Thanos is dead, when we cut to the barren surface of Titan, where Thanos is living as a simple farmer, trying to restore life to Titan one plant at a time. At least until Adam Warlock shows up, and then Thanos allies with him against some new threat.