Well, of course I don't expect this to happen, but it seems a good way to bring players back and let the server always recycling players.
A player who reach lvl 150 (tatics wont be needed to this) can reset their lvl to 1 again, but with a bonus of stats.
Simple as this. It's just a point I wanted to show. Hardly will be accepted, but well, whatever.
PS: This idea can be more studied.