Bows flee from shooting by war wagons. However, foot can only leave a PF via a gate, so the bow would not be able to flee out of the tower if there was no gate. In that case I assume it would stop after the recoil.
Your question would also apply if the shooters are bows or shot.
You cannot recoil across fortifications you have not previously crossed. Therefore it would be unable to recoil a second time.
I note that a recoil from a PF wall-walk is a base width, not depth, but AFAIK a tower is not a wall-walk.