Considering the Marine and Noir were sent back in time specifically to prevent Earth being invade its almost certain that the Usurpers win the war.
Still the idea that the Usurpers possibly could lose is interesting, which is why I'm going to shoehorn in a link to the Post War Collection trello because I am a menace
https://trello.com/b/1aV5OBGd/pb2-post-war-collection.
Essentially this explores the timeline where the Usurpers lose, but barely, leaving Earth in ruins while communications between Earth and its colonies are mostly severed. There are plenty of Usurpers still around but there are also numerous factions that exist in the wake of the war. The Marine, Noir Lime, and Proxy also do not manage to go back to the past in this timeline, so exploring their story will be interesting whenever I get around to it
It's really WIP and I plan on redoing a lot of the existing lore to make it more concise and higher quality. There's also a lot of recent drafts in some of the comments. It's an artist collaboration project so folks who want to contribute are welcome to send me a message.