This is a situation where no matter what happens, both these people walk out winners. The losers are the ones who are cursing and abusing each other on social media over what will happen come Saturday.
McGregor is in it for the money and increasing his brand value to Mayweather's league. If there's anything we know for sure about Connor, other than that he is an absolute asshole, it's that this guy loves his money. Seeing the kind of money a Mayweather fight pulls, he is definitely interested. Even if he loses this fight, he (a) gets a huge payday and publicity, (b) has the excuse that this wasn't the sport he specialises in, and (c) will defeat a few guys in UFC and easily leave this in the past with his brash attitude.
As for Mayweather, he has nothing left to prove. His in-ring stats are exceptional. Given the way he has conducted himself over the course of this build-up, and especially the final press conference, even if he loses he remains a respected figure and not become the butt-of-jokes.
As for me, I'll just go watch the highlights the next morning, and read hysterical comments by the losers mentioned earlier.