In a new interview with IGN, Star Wars: The Last Jedi's Mark Hamill has revealed George Lucas' original plans for Luke Skywalker. Believe it or not, they are substantially different from what actually happened in Star Wars: The Last Jedi, a film George Lucas had no creative input on.
"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]."
IGN does not have Hamill elaborating on the above (though they do point out that Lucas wrote "a new treatment for a sequel trilogy as the series transitioned into becoming a Disney property, but Kathleen Kennedy scrapped the majority of his ideas in favour of J.J. Abrams and Lawrence Kasdan's Force Awakens script"), which leaves us with some unpacking to do.
If we're taking all of this at face value, it sounds like Lucas would have kept Luke Skywalker alive throughout the newest Star Wars trilogy, training his sister in the ways of the Force, and then cashing in life's chips at the end of Episode IX. This is an interesting alternative to consider, but how you feel about it will probably depend on how you feel about Rian Johnson's take on the material, which found Leia already handy in the ways of the Force and Luke wrapping up his run at the end of Episode VIII.
Given the divided response to The Last Jedi, we're guessing you folks will have your own opinions on this matter, and encourage you to share them in the comments section below (for what it's worth, we have zero complaints in regards to Skywalker's fate in The Last Jedi and think Rian Johnson crushed it, but what do we know?).