I just nearly had this happen in a game. Some people said the game ends in a tie and no one wins. Someone (and that someone was Landstander) said the game ends in an automatic town win. The only people left were Townies, Cultists, and a Jester (me).
So what does happen? Or is that something you can manually define in the rules.
PS: Landstander you rage something fierce in game don't you? And just asking Arson/Cultists to give up for the win. Shame on you.