No, not brute force. That's obvious and it's been done (see any film with "Damned" in the title). What would bring them down (if I were writing it) would be the discovery that despite their pretensions they do still have all the emotional apparatus that humans have, and because they put no value on it they have never learned to govern and use it properly. Sir Terry knew that you couldn't have two Grannies Weatherwax, and here we would have a whole (alleged) new species of them. They would be at each other's throats (in a thoroughly coldly rational way) as soon as the novelty of finding people like them wore off.

I expect that in these books they will turn into godlike beings of ultimate enlightenment (by their own lights) and go off to create a new and much more efficiently run universe somewhere. One thing that even these authors cannot escape is that writing about such creatures successfully interacting with each other, without any leavening of actual humanity, would be BORING. Imagine an all-Vulcan Enterprise.