In a new interview with IGN, Hamill takes a break from discussing his creative process with The Last Jedi director Rian Johnson, instead shifting to reveal the ultimate fate of Luke Skywalker in Lucas’ original plans for the sequel trilogy, which he never got around to making after the negative response to the prequels:
“I happen to know that George didn’t kill Luke until the end of [Episode] 9, after he trained Leia. Which is another thread that was never played upon [in The Last Jedi].”
So not only do we learn that Luke would have died at the conclusion of the trilogy, but that Lucas was bullish on incorporating Leia being trained as a Jedi—something that happened in the extended universe—by her own brother.
Of course, in reality, Disney took over, Kathleen Kennedy pretty much threw out everything Lucas suggested, and Episodes 7-9 went in a very different direction. So, yes, none of this really matters outside of a “What if?” thought experiment, but since idle speculation about Star Wars is the motor oil of the internet’s engine, this should keep it humming along until the next spoiler about J.J. Abrams’ script for Episode 9.