While Cheby could be mafia and Cassandra, I don't see any reason to off them. The fact that cassandra has never been mafia before doesn't change the fact that Cheby is statistically more likely to be town (Gambler's Fallacy). The cassandra has the potential to give beneficial information to town. We would be doing the mafia a favor by taking out Cheb. If the mafia doesn't eventually take out Cheb, then the concern that cheb is mafia becomes real. For now, don't think it matters if cheb is or isn't mafia, they are a net benefit to the town.