Georges St-Pierre has won the UFC welterweight title twice, defended it an astounding eight times, and pretty much done it all in MMA. I'd say that for GSP the only thing he has left to do is defeat Johny Hendricks at welterweight, and if he accomplishes that, go forth and try and fight Anderson Silva in a superfight. I think GSP is the type of guy who wants to go out as the greatest of all time and for him to do that he will need to fight Anderson Silva. The one caveat to that statement is if Anderson Silva defeats Chris Weidman. Weidman is hell bent on messing up all superfights and defeating Silva to win the title. Should Weidman pull off the upset, then a superfight between Pierre and Silva can be put on ice. However, assuming that the odds do come into reality and Pierre beats Hendricks and Silva beats Weidman, then I believe GSP should fight Silva and retire after that, win or lose.
From there the next generation of stars will get a crack at the belt, and his teammate Rory MacDonald can finally challenge for the welterweight title and possibly continue the legacy of Canadian champions in the UFC at 170 pounds.