I think that it will come down to how long McGregor can stay on his feet and he has proven that he is quite adept at staying alive. Mayweather tends to dance around out of arm's/harm's reach and moves in after thought has been given to the attack with one of the hardest punches in the business. McGregor rushes in like a savage bull, employs some strategy and thinking, but also has a wicked left. McGregor has youth on his side but it will be difficult for him to transition to pure boxing given the instinct that must come with being a world class mixed martial arts fighter and the tendency to use one's feet. McGregor could get a lucky punch in and set the pace. Landing one or two punches will certainly lend longevity to his time in the ring.