My crazy neighbor is being eerily silent, is this good or bad?

I strongly recommend you make a formal statement to the police rather than a casual chat with the sheriff. Your neighbour may have caused himself serious harm if he's gone quiet and not emerged from his flat for a while but you should most certainly be on your guard. You absolutely must go over this with the police again and demand action because quite frankly, I'M scared by your question and I don't have to live near him.