User blog comment:Mlgrsd/How could Lucifer land in this dungeon?/@comment-1031724-20170218044521/@comment-1031724-20170218161542

Lucifer killed Gabriel with an angel blade

Crowley we can at least count on to stay around coz he's one of two fan-favorites they won't kill, redemption or not.

Just saying, starting after Abaddon they haven't killed any main villains without either reforming them first or reviving them after, and I think it's intentional. So, Lucifer's only chance of death is redemption, and since that's impossible, he's sure to survive.