All questions are worth asking! TIMELINE.EXE does indeed find the most energy-efficient outcome! In this case, unlike with the goblins, it's not just a matter of missed resources, nor a case of simple equivalent exchange—the goddesses' existences themselves drain the planet. Even if the Nalawi's Gifts, as well as Nalanni and Ryba's entire stores of power were somehow re-routed into the land, just sustaining Ryba and Nalanni's bodies would take up more energy than the planet could renew.