Vitali should retire if he's not going to vacate, but continue to fight the Charrs of this world.
Haye should retire because I dislike him.
(That's a joke. I don't give a **** what he does.)
I see no reason for Wladimir to retire. You may not approve of his style, but he is a great champion. Very professional and classy, I'd love to see someone manage to challenge him, although I doubt that day will come anytime soon.