Damned if we don't only if he is in fact mafia. If he's town, he might not even be killed at night. Favor is not alignment, and he only detects favor. While it's likely there is some use for such a role, it doesn't detect mafia. (And, btw, because of that, it is strongly implied that he does have the ability he claims, even if he is mafia, because mafia shouldn't be able to guess that very easily. Now if you and/or ATPG have been running around telling your character names or if you are also mafia, then that's different. Note also that his result doesn't clear either of you of being mafia.)

Damned if we do ... well at the moment I think he's likelier to be town than not, so I'm with you there.