Severe respiratory infection is what you have. I'm afraid that months is too long to go without treatment and correction of the poor environmental conditions that caused it. The snake is probably too far gone but needs a vet / antibiotics and proper temps/humidity ASAP or it will die in my opinion. The length of time he's been sick doesn't matter. RI's don't go away and without antibiotics and proper care, pronto, death by RI is inevitble. Just a matter of time.

As to the question, if you have to ask, then no, don't brumate. I tell that to everyone. If there was a good reason to brumate, you would know what it is, and therefore not need to ask the question. "should I...."