[ano]

I'd second Hadrian here. Frankly speaking, I nearly never had to quit early and at later stages defeat may become absolutely obvious when you still have a lot of land. It will take a long time to kill you but that is decided for sure. You were in similar situation, Baalz, if I remember what I read correctly, in Artifacts game. You even had a Forge and everybody thought you're perfectly fine while you knew you had absolutely no chance of anything. So, probably, things are a bit more complicated here.
Personally I will lose all interest in the game when, say, something weird happens at first turns (plague, Bogus or mandragora attack on turn 2 is the most obvious). Who knows, how long it takes for others to kill you after that? A year? Or maybe two? Will you perform much better than AI? I doubt it.
I'd say I agree to do everything I can when it makes sense and also to find a sub when it doesn't. Also, I'd agree to make reasonable effort to make game more interesting for others even when it loses interest for me. But definitely this is not fighting till the last breath (or even the capital).