Google may or may not stop paying Mozilla as part of the antitrust scrutiny. I have no idea if there's actual reporting to this effect, or any form of legal analysis suggesting this is the most plausible outcome. If anything, antitrust scrutiny might lead to this funding being more secure and more robust.
So this might not happen, but this whole threads carrying on like it's a fait accompli.
Hold on, why are we talking about this like it's something that's not happening? There's all kinds of forks of Firefox.