I understand that scenario, and I think that the GM should probably call it on a case-by-case basis. If the JL has all of the remaining villagers together, and they have a powerful group of traits left: Leader, Hunter, Brutal, OEO, GA, something like that, then why penalize them by ending a game that they could potentially win?Well, "parity" reached is just a winning condition that we've agreed on as a community.
I reckon you could even have a scenario where there are 2 villagers and 4 wolves left, and the villagers could somehow turn it around. But then the winning condition would have to be "wipe out all villagers" or "wipe out all wolves". In 99.9% of cases, this would just unnecessarily prolong the game for a few days.