Thing is we have let players who left the code to play another sport before like SBW, Benji and RTS return to the game. So what is different about this comp? More money? I'm not sure given the previous allowances, the NRL also taking Rugby players, that they would have much of a leg to stand on. It basicially just comes back to restraint of trade.
Either way, if a Haas left and then decided he wanted to come back and play NRL, do you really think PVL would stand in his way? Not a chance. If you are good enough, the NRL will always open the door again.