Is it just me or the fact that Vulcan left the Federation seemed to be the tipping point for maybe the Federation is beyond repair.
Andoria, Earth, Vulcan, and Tellar were the founders of the Federation. Andoria has been confirmed to be with the Emerald Chain, although possibly not by choice (The chain might have just taken them over, but regardless it doesn't seem like Vance is trying to "save" Andoria). Vulcan and Earth outright left. What does that leave, Tellar of the founding races?
Even if interstellar travel is restored, the loss of three quarters of your founding team is a huge morale blow. Even if they say, ok, we'll come back--I mean, that mistrust will still be there. Look how much international drama came out of just the UK leaving the European Union. How is the Fed supposed to come back from the loss of all but one of their founders? How can they convince anyone to rejoin when they'll all say, "If Earth can do without the Fed, if Vulcan can do without the Fed, maybe we can too".