Thanos is coming back to the MCU. In actual fact, Thanos might be coming back to the MCU twice in the space of less than two years as part of Phase 4.
Considering the fact that we saw him die twice in Avengers: Endgame, him returning at all is possibly quite confusing for more casual fans, but it comes down to the timeline being all screwy now.
He's first rumoured to be reappearing in Eternals as a younger man, which would make sense given his link to those characters and then he's got the small matter of the Disney+ show What If...? for which Josh Brolin is returning to lend his voice.
Crucially, both of those projects are set before his death in Endgame and despite calls for him to return based on how well Brolin's performance went over with fans, he's just not going to return.
There might be a precedent in the MCU for characters returning from the dead, but the most important thing is that any death that has carried real narrative weight hasn't been undone (well, maybe Gamora, but we can give them one exception). Vision, Killmonger, Tony Stark, Quicksilver, and Black Widow all remain dead and while two of them WILL return (Vision's return is a strange one because it may not be rooted in reality and Widow's is set in the past), they won't undo really important emotional moments.
That's what will keep Thanos in his grave and it's an idea that has been confirmed by Endgame writers Stephen McFeely and Christopher Markus who said that they wouldn't want to undercut the impact of his final moments by undoing them:
“It totally depends on your opinion of the multiverse and how you’re going to go forward with the idea of using characters who are gone, right? Certainly, comic book readers are pretty down with that. ‘Any way you can give me that character, give it to me.’ My grandmother’s not down with that. She knows Tony died. She knows that Thanos died. ‘Why is he back?’ … So the question becomes, what path will Marvel take going forward? I love the idea that things matter. They stick, and you don’t get a lot of get out of jail free cards.”
By that logic, there is no way that Thanos can come back. Resurrecting him would undo his arc, given that the older version of the Mad Titan was very willing to sacrifice himself to achieve his goals of "saving the universe" - it was that singular commitment that defined him, that ensured he was perversely empathetic and which tied him closely to Tony Stark. All of those things were what made him and the Infinity Saga so compelling.
Undo it and you undermine the greatest story the MCU has ever told. So let's hope it's not going to happen.