Eh, this will also prevent others from attacking the Hero, anyway. I cannot cast ethereal staying corporeal. But maybe I should say they just treat him as a pacifist? ^^
And this fint with locked spellbooks... maybe it would be better to give Hero a powerup item wih the ability (which will be used instantly, even no inventory space is required), but will it stay long? How can we mark the time of re-corporeating?