Depends. If one player suffers from barbarian hordes (or, even better, those evil knights), a temple and a lab burndown during the first four turns, I'd be all for a mulligan. That game is certainly over for him.
From everything else, even only two of those events, there's a comeback.
I usually take order 2 luck 3 or order 3 luck 2 to prevent these things from happening.
No, really, I do.