The Einzberns hire Kiritsugu. Some random mage hunter guy.
As far as I'm concerned, the Einzberns pretend to use the Grail to restore the Third Magic thing.
But, if Kiritsugu uses the Grail for his wish (the world peace thing), won't the Grail vanish?
So the question is, what were the Einzberns planning to do once Kiritsugu won the war? Don't they need the Grail to get the Third Magic thing?