If Pacquiao wins without controversy, he retires. He'll have nothing more to prove. Only if he wins in controversial circumstances would a rematch with Mayweather be enough to tempt him back.

If Mayweather wins, he will have a rematch with Pacquiao if it's close enough or controversial, or he will fight Shane Mosley if he beats Berto. If Berto wins, he may fight him if there's enough hype around Berto from HBO (which I suspect there might be).