I have a friend who completely focused his ankle skating and had multiple surgerys. He was told if he fucked it up again he probably wouldn't be able to walk properly for the rest of his life. So he pretty much had to quit skating because of the risk to his fucked up ankle.
He still loves skating, and wishes he could skate so bad, but physically he can't. Dunno if that makes him a lifer or watever, but it sucks.
Also, a friend of my brothers was the biggest skate rat and had a brain anyurism that fucked up his motor skills so now he walks with a cane. He still loves skating so much though and its seriously the saddest thing, I can't even talk about skating too much around him because i feel like I'm gonna bum him out. He always brings it up though, and wants to watch me skate whenever I'm around, so I do, but you can tell he wants back on the board so bad.
So yea, people who skated and had to stop due to physical ailments can be lifers in my opinion.