If we believe there is no Mafia, however, and since there isn't likely a cop at all in this game, what possible reason would there be to have a Death Miller? Is there any reason to beleive that role would flip insane on investigation in this game?

Honestly, it makes next to no sense for this game to even have a death miller. So why should we believe his claim?

Also, I've seen games lost on the premise that town thought the Mafia wouldn't be stupid enough to do something, so I don't take that as a legitimate reason. ;P