It's a little odd that he hasn't peed or left urates at all in the last 4 months. Do you ever observe him drinking?

A vet is obviously the best decision. He is probably lethargic from being cold for a while. It's probably too late, but you should have warmed him up slowly so you don't shock his system.

If he is alert and moving around on his own, tongue flicking and what not, I'd say he is probably going to be okay. Do you have any pics?