No one's ever really gone. Luke Skywalker says it himself in the first teaser for Star Wars: The Rise of Skywalker. Or at least his voice says it. We don't see Mark Hamill in the trailer, but we know he'll be in Episode IX, the final film in the Skywalker Saga. That was already revealed, but it wasn't clear how he would be shown in the final movie, since Luke died in Star Wars: The Last Jedi.
However, if you can believe anything Mark Hamill says when promoting movies, it sounds like he confirmed Luke will return in the final movie as as Force ghost.
You could consider that an early spoiler, or maybe just an acknowledgement of that "peculiar" tradition of the Star Wars galaxy. If you're a Jedi, you can always come back as a Force ghost. (Sorry, Han, it sounds like you're out of luck.)
Here's what Mark Hamill said when asked if The Rise of Skywalker would really be his last Star Wars film:
I sure hope so. [laughs] I had closure in the last one, you know? The fact that I'm involved in any capacity is only because of that peculiar aspect of the Star Wars mythology where if you're a Jedi you get to come back [and] make a curtain call as a Force ghost.
It's sad that he's eager to be finished with the Star Wars galaxy, after more than 40 years as its #1 hero. But it's also understandable, and he has spoken in the past about experiencing Star Wars fatigue himself, to a certain degree.
Sounds like Star Wars fans shouldn't expect a new twist where Luke didn't actually die in Star Wars: Episode VIII. If Mark Hamill wasn't just joking around to the AP, he confirmed that Episode IX - The Rise of Skywalker will see him return as a Force ghost -- ala Anakin, Yoda, and Obi-Wan at at the end of Return of the Jedi.
Luke's Rise of Skywalker trailer voiceover includes these words toward the start:
We've passed on all we know. A thousand generations live in you now. But this is your fight.
Is Luke saying that to Rey, or Kylo, or a group of young Jedis? Others? Later in the teaser, we hear more words from Mark Hamill's Luke, probably from the same continued conversation:
We'll always be with you. No one's ever really gone.
Does Luke say those words as a Force ghost, appearing to Rey?
Mark Hamill was initially vocal with his doubts on the direction of Luke Skywalker's storyline in Rian Johnson's Star Wars: The Last Jedi. He also said he had pitched a scene to The Force Awakens director J.J. Abrams, allowing Luke and Leia to reunite on screen and having them together before Han Solo died. He's really upset that the original trilogy trio never got to reunite in the new movies; and now that Han is dead on screen and actress Carrie Fisher is dead in real life, they lost that chance.
Then again, no one is ever really gone. We know Leia will still return in Star Wars: The Rise of Skywalker, and it's too soon for fans to judge how Luke's storyline will play out in the final movie. (Not that that will stop anyone.) The Rise of Skywalker opens in theaters on December 20.