This fight is a whole helluva lot more important to their actual legacies (especially Mayweather, since he really could end up being considered the greatest fighter ever with this generation and people will always look for ways to turn him down) than it does for the overall sport. This fight will bring crazy attention to the sport... FOR THIS FIGHT... but it won't do anything for its future (unless Pac wins or Floyd wins a very close fight and it can set up a rematch). A couple of years from now though and this fight won't mean anything. These guys aren't young enough to build a future off of this fight, they're both headed towards the end.
It'd be bigger for the sport if some young gun took out either one of these guys.
Boxing doesn't actual need "saving" though, but even if it did one fight wouldn't save it.