Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Peanut has horrible dental disease and now what appears to be a fractured jaw.
Even with horribly bad infections it is very unlikely that the jaw would fracture. It may be painful, and there may be infection in the bone, but a secondary fracture would be almost unheard of.
When we see a jaw weak enough to fracture more likely causes include abnormal calcium metabolism due to internal organ failure (kidney disease and secondary "rubber jaw") or a tumor in the jaw which weakened the bone integrity and allowed it to fracture with minimal stress.
Even is this were a fracture secondary to an infection we would need to remove the residual infected bone, place antibiotic implants, and wire his jaw shut to stabilize the site. It would not heal without significant surgical and medical intervention.
I think his hiding and wanting to be left alone more signify significant pain. I understand that this may not be what you want to hear but Peanut needs to see his veterinarian, and euthanasia may be the kindest option. Dogs do their best to cope with whatever sickness is thrown their way, and he must be a tough fellow to have made it to 16 years of age, but he needs hands on veterinary help now.
Please let me know if you have any further questions.