Idk why people are worried about Luke dying in future movies. If they kill Luke in TLJ (or later), they’ll surely Force Ghost him and he’ll still be there, just bluer and less opaque.
Luke as a Force Ghost would be cool, if it were to ever happen. As a Force Ghost, Luke would still be helping out with the knowledge he gained over the years. Though, he’d probably have Yoda on his back, because he’s training Luke, to perfect his Force Ghost.
Perfection.