I don't see any reason he couldn't go back to 140 after a loss. In fact, he may well head back down even if he pulls the upset. He has to be careful about fighting at 147, but the problems come against big, true welterweights like Collazo who he can't out muscle. Mayweather is a naturally smaller man, and is still only around 150 on fight night even at welter, so I don't see how the fight at 147 will be any factor.