I think it is extremely unlikely Luke is alive. There is no good reason we need him to be alive and it would bring about an unnecessary debate about wether or not coming back from death is a Dark Side ability.
There are a number of possibilities that do not involve Luke coming back from the dead.
1. Ben Solo, who is half Skywalker, could return, destroying Kylo Ren internally as Anakin did with Vader, and save the galaxy from Darth Siddons. If this is it, it is probably would not be as direct as I just outlined it, but, instead, some sort of modern, nuanced reemergence that still leaves us guessing a bit.
2. We find out that Rey is a Skywalker. I think this is very possible, but not that she is the daughter of Luke, or anything like that. Most likely she is a clone of Palpatine and Anakin. This would be some large cling operation from the Empire days that produced a bunch of clones and then rejected some, or perhaps shut down leaving Rey as a little girl in the hands of whoever would pay.
3. Rey starts the SkyWalker Knights, or something like that, that would be a new version of the Jedi. I wrote all the detail of that here: What Could “The Rise of Skywalker” Mean?
This post is based on my Quora answer here:
Will Luke rise again in StarWars: The Rise of Skywalker?Answered Apr 14
