MP Game: How bad is too bad?

[thejeff]

But again, by that point the damage has mostly been done. His neighbors have already gotten the extra territory that A should have taken. The only difference is that they had to fight a bit more to take the capital from B. Two nations squabbling over the spoils could play the same role.

I think I'm swinging even more to the "No forcing anyone out" position. Maybe not in a perfect situation, where you have a disinterested party who can know the whole situation make the call, but in a real game, everyone has an interest and those in the position to best judge are also those most likely to be affected.
Long before actually subbing anyone, I'd contact them and see if they thought they were out of their depth and were willing to back out. And I'm sufficiently non-confrontational that I'd wait too long for that anyway.