When you're determining the GOAT in a sport like boxing it comes down to opinion... even if they were in the same era there's no way Floyd could fight Muhammad Ali so it's hard to just decide one is definitively better than the other. And then there's the whole styles make matchups thing, and some boxers fight other boxers at the right time (for example, Joe Calzaghe beat both Bernard Hopkins and Roy Jones Jr. but you're not going to find anybody who'll say Calzaghe is higher on the all-time list than either of those fighters).
I say all of that to say this, if Mayweather wins he has a legitimate claim for GOAT. If this fight never occurred, Mayweather has a legitimate claim for the best of all-time... he'd be considered the best of his era but there'd always be that cloud held over his head. If Mayweather loses, because of the way he has shaped his own narrative behind the fact that he's undefeated, all of that GOAT shyt goes out of the window and a good number of people (probably the majority of boxing people) will have Pacquiao held over Mayweather. If Mayweather was going to take a loss, it needed to be a lot earlier in his career so he could recover and show how well he can come back. At this point if he loses I'm not even sure if mentally he'll be able to handle it... I'd seriously consider putting him on suicide watch.
Long story short, he's in the discussion if he wins. If he loses, probably not so much.
