> From a more down to Earth perspective, if I left the planet on a one-way interstellar FTL journey, confident I would never return and that there was no way to communicate with the people I left behind, even though it would be a relief in some ways and I'd stop caring about people left behind, I'd still want to arrange good things for some of them after my departure. Because I'm nice like that.

Well, you can't be so sure you'll never see them again and you'll never be able to communicate with them, because of scientific advances and such. The only truly irreversible thing that could happen to a human being is death itself. Everything else being reversible (or eventually reversible) is the nice part about being alive.