Hello, Welcome to Just Answer and thanks for your question. If he cannot void, he has severe urinary retention and needs to be catheterized.
I mean if he cannot pee (void is the polite word), then he has urinary retention.
The risk of not having surgery is probably greater than the risk of anesthesia. Only his treating doctors can evaluate his respiratory status and determine if he is a candidate for a respiratory anesthesia or spinal anesthesia.
Prostate surgery takes as long as it takes. It depends on the patient, the surgeon, and what type of surgery (open, laparoscopic, robot-assisted) kind and approach of surgery is chosen by the surgeon.