Oh noez? He's a good player, but him leaving isn't the end of Brawl, not by a long shot. Even if all the good players quit simultaneously, other players will come along and take up the spots left. This game is too huge to die anytime soon. (Though his reasons for quitting were sound)
The thing that you were talking about, Thibault, with Diddy doing a very long Up-Smash has actually been brought up before. We've failed to reproduce it, though it is very impressive to see. Here's a video (not the best one; there's one called "Wat" that I can't find that is a lot better):
http://www.youtube.com/watch?v=g3I-3DfjEcs