I still don't think McGregor will win, but the notion that he has no chance is ridiculous, IMHO. A lot of people said the same thing about Brock Lesnar when he transitioned over from wrestling to MMA briefly, and he won a title. Similarly, the same thing was said about Daniel Cormier, who was an All-American wrestler in college and an Olympian. People said just because he was a good wrestler didn't mean he could take a punch. And he won a title.
It's a combat sport, so McGregor isn't an "amateur" when it comes to punching. I realize boxing and MMA are different, and honestly that's why I think McGregor stands a chance. He doesn't have to worry about getting taken down, doesn't have to worry about getting kicked in the thigh.
That said, I think Mayweather will out-class him. McGregor will try to land the big shots that he can get away with throwing in an MMA fight and he'll tire out. I don't see Mayweather knocking him out, but instead taking a decision win that will probably feature about six or seven really boring rounds of McGregor attempting to stalk Mayweather only to get peppered with counter-punches.