I don't see a reason for it. If Morales wins they both should go thier seperate ways. If Pacquiao loses he should do everything possible to fight Barrera.
Obviously if Pac gets this there will be a third fight. But what if he loses?
No point. There are never trilogies when a fighter loses 2 in a row. Im not sure even Pacman would want to fight him a 3rd time if he loses...