It's got to go one of two ways because I cannot see McGregor lasting pass the 8th round after getting peppered from jump street. Death by a thousand cuts sort of thing for McGregor if he doesn't clip Mayweather clean and early.
That said, don't count out McGregor completely. Mayweather is 40 and using 8 oz gloves against a guy with astounding power for his size. Unfortunately, I believe McGregor will gas and eventually the ref will stop it between rounds 6-8 but you never know boys. It won't go to the judges.