Well, canonically Glastig Ulaine decided she was gonna try her hand at human genocide right before Yamada talked her out of it, and being by far the most powerful person in the world immediately after the Golden Morning, she probably would have succeeded.
The other thing that has to be remembered is that the Golden Morning doesn't have to play out well because Cauldron has no means to predict the course of the battle, and no way to put a finger on the scales like they normally do. They're so used to being able to do both, as well, that this could really bite them. They think if they do it early the result will be better...but it's a lowercase t, not an uppercase one. There is no real certainty of success. If the story ended with Khepri, Contessa, and three other people standing in the ruins of a dead planet that's rapidly going to kill them all through tectonic activity or an unbreathable atmosphere or a simple lack of food or water, that's a possible outcome too. The world's not over. It's just going to be very very soon.