When are we supposed to stop fighting?

[Absimiliard]

Zodiark doesn't seem to have much, if any, will of His own. Without a 'heart' He seems content to just chill out in the primal equivalent of sleep mode. Also, if I recall correctly, the sacrifice plan was being formulated while Elidibus was still in Zodiark, the arguments about going ahead with it are what caused him to withdraw himself from Zodiark.

Now I am kind of suspicious that Elidibus reappearance suddenly quells the majority of the dissent, but I don't really doubt that Zodiark would have held up His end of the bargain to the best of His ability. I would probably be more suspicous that it's just a ploy for more aether if Zodiark was the only Ancient primal, but Hydaelyn never seems particularly aether hungry either, and they're almost certainly more similar to each other than they are to modern primals.

It wasn't so much that Zodiark was content to sit in primal sleep mode as it was he had no choice in the matter. Sundered and bound as he was, there was simply no way he could act. The separation of Elidibus did to some extent deprive him of his own will, but he did retain his instincts -- and those instincts told him to be free. He was also still beholden to the urgings of the Ancient souls within, whose motivations remained, above all else, the preservation and restoration of Etheirys and her people.

As for aether; Zodiark contained the souls and combined aether of innumerable Ancients. It seems rather likely he might not even have been capable of running out in the first place. Hydaelyn was created using a much smaller number of sacrifices, and we've seen several times over the course of the game the decline in her abilities as her aether reserves dwindled. It was this depleted state that ultimately forced her to claim Minfilia, just as it forced her to utilize Krile a handful of times. We learn during the battle with her that she kept back just enough aether to be able to fight us with her full power exactly one time. It's not always immediately evident, but there are times (again, Minfilia and her trip to the First being the prime example) where Hydaelyn did take steps to acquire more aether.