Ok, I'm here to give it a shot. I also asked my wife who survived massive injuries in a head on collision car accident years before I met her.
First the points that you gave
1.) If the accident was severe enough and he sustained severe head trauma, it is plausible that the hypothalamus could also have been injured. Not only does it regulate body temperature , but a whole host of neurosecretions are done there regulating certain metabolic reactions. Look up hypothalamaus for the specific details.
2.)People who have had and survived severe head trauma's have reported many different things. My wife's injuries were such that she doesn't remember what she did, but for several days she was alert, but, behaving in certain ways that she became "a legend" in the intensive care unit". Lecturing the nurses on the meds they were giving her (she is a pharmacist FYI) and other personality changes, until she "came to". So it is plausible for someone to be in a coma, come out of it and remember what people said while they were in the coma. As for being "asleep" it is an accepted medical practice to induce a "coma" to keep the person still and give treatments and procedures time to work. So the just being asleep part, kinda doesn't ring true for me. But, it is fiction, so go with what works.
3.) Holding off surgery,...if the person is unstable, you only want to do what is necessary to stabilize a person's vital signs. Which is what they did in my wife's case. She nearly lost her leg to the fact that the bones were shattered, but, they held off the surgeries until she was stronger. As it was she needed multiple surgeries on that leg to save it.
4.) The fever going down, very plausible. As IV fluids and medications kick in.
5.)Sent into surgery and dies.....very plausible, if the trauma/injuries are extensive enough, especially with trauma to the hypothalamus, it's conceivable that things just start to cascade out of control, to the point of no return, almost like a domino effect. But, it wouldn't be just related to the fever, the fever would be a part of, but, not the sole reason for death. My wife did mention that she developed, what the surgeons called "Bone Fever", that caused some delay in her care. She herself is unclear what it meant.
The thing to remember, is that fever is one of the bodies defense mechanisms against infection.
I remember once, a stroke patient that I took care of had a massive amount of damage done to the area near the brain stem and that also wreaked havoc with the patients body temperature with out of control fevers.
