It could have a rematch (even if there is no written clause in the initial contract), if the fight is going to be razor sharp close or maybe even in a draw.
But if it's a convincing win, then maybe not, but if there is a huge money involved then again, they could go and fight one more before going up in weight. So I guess the fans will also have a final say and maybe the promoters are going to take that lead from us if they see a demand for it.
We never know, because that always depends on the winner if he will give a rematch, that's why to ensure a rematch will happen, it should be written in the contract. One example is the fight between Mayweather and Pacman, for some, they think it was a close fight, and both could make huge money again if Mayweather gave a rematch, but he choose not to fight again just to ensure he will keep his undefeated record.
Right, I would say that the public will demand for it if the fight is close, but we will have to see how the first fight is going to be good. Although they have both plans to move up in 154 lbs chances are they will have to wait for the pulse of the boxing fans regardless of who is going to win. Mayweather is afraid that he will lost in the rematch because Manny is not 100% that's why he refuses and just ok with doing some exhibitions to make the same money, less risk for Floyd.