This attitude is exactly why if I was the mod in question, I would just ditch the account. You're asking them to prove a negative, no amount of proof they could provide would ever be enough. They'd be forever hounded by internet lunatics.
Not at all. A single post on the account would be enough to completely disprove the theory. The whole reason the theory exists is that the account was previously extremely active, and all activity stopped abruptly when Maxwell was arrested. I don’t think you can say “no amount of proof would ever be enough” when no proof at all has been provided.