Never. Mayweather never throws that many shots never. Also Pacquiao of late doesn't fight for the full 3 minutes of the round either. I don't believe we would see the 12th round either....imho Pacquiao would be getting out boxed and probably due to his aggressiveness would get stopped before 12.
No way it would be anywhere near as exciting. After a few intense 4 rounds, it would be all Mayweather after that IMO.