I have never liked that Kylo was visited by a non-force user, in this case Han Solo. Whether it was all in his head or not.

What if… THIS is what kills Luke, just like it kills Leia. Either Leia was too weak to do it by herself, or it just took the two of them to conjure up Han Solo’s essence in Kylo. I would accept the fact that Luke went to Ahch-To to die, because he knew that he would be sacrificing himself to save Kylo.

In this instance, he dies WITH his sister. MUCH better than a death to provide escape for a small group of fighters on Crait. It could even be explained that bringing someone back from the dead even temporarily, is against the will of the force and the force took their lives as the price. Even THAT is a better explanation than what we got in Last Jedi.

It ALSO brings the Big 3 together one last time… kind of…