Schumi probably pulled off some of the most impressive wins iv seen, and leaving while he's still damn good is probably the best way. still won't forgive him for robbing the championship from Hill in '94 though, other than that its been great watching him race.
As for F1 without him, next year will still be great, with Alonso, Raikonnen and possibly Button putting in a decent chance at the title (assuming Honda improves over the winter) and with only 1 tyre supplier, so races won't be decided on whos running bridgestone and whos running michelin.
The only other thing i'd want Michael to drive in now is the world rally championship...being amzing in an F1 car is one thing, bt being amzing in a rally car is completely different level of amazingness.