Luke's primary trait, that seperates him from the Jedi of Old, is his compasion. His "faith in his friends" is his weekness, as the Emperor Himself points out. Thirty years on, can Luke do what Anakin could not? Accept the loss of a friend or a loved one? Or would he go to ANY length to save them. He pushed aside his Jedi training to recklessly try and save Han and Leia on Bespin.... He is wiser, and more mature now, but if the stakes were high enough? The question of immortallity/the netherworld of the force is one of the few unanswered questions that run through both the PT and OT, it is one of the few threads that can narratively tie into the ST. Thematically it ties in with aging heroes and generations down the line. Can Luke learn to let go...? Of his friends? Of his accomplishments? Of the galaxy he helped rebuild? Of life, itself? Or will the desire for things to be the same, of his friends staying together... be the seed of his undoing?