If a house is down to a single unit (either a Power Token or Hero) on the Map, that unit cannot, for any reason, leave the Map. That unit cannot attack alone, be attacked by other players, or be eliminated by an event. This is true for units of both player and non-player houses. However, that final unit may battle, and be battled, if it shares its domain with at least 1 ally’s unit that is not the last unit on the map of that allied house.