If it weren't for the arrival of Genizix, would humanity have been able to restore Earth, or was it doomed either way? On a related note, how common is it for a civilization to let their biosphere deteriorate like that in this setting? Is it fairly common, or were we uniquely stupid in that way?
There was little hope for Earth even before Genizix arrived. It was in the middle of a climate crisis, one which had already caused irreversible damage. Humanity would not have survived for much longer.
I mentioned tipping points in another post - here's an excerpt from a Wikipedia article that explains it well. Vivere 44 is fictional, but the possibility of this happening is very real.
As for how common this is throughout the universe, it has definitely happened before to extraterrestrial civilizations. In the Zhagaviit solar system, where the beginning of the story is set, there are strict regulations on climate management. The Wider Galactic Community keeps a close eye on all registered planets in order to prevent disasters.
Unfortunately for Earth, Genizix found it before the WGC did.
