Bill, you always have the most thought provoking cases. Amazing.
I’m not going to answer the HBOT question … though it seems most straight forward.
Here would be my approach, and I would not begin with HBOT. My interest in your presentation is “some residual bone exposure” … Much like mandibular osteoradionecrosis, all of the devitalized bone must be extirpated … or HBOT has no effect.
Other key statements — you stated that there was a good granulation base. Excellent, but I think you’ve got dead bone as your primary problem.
I would ask the plastic surgeon to go back in and debride (with a burr tip) every bit of devitalized bone. Also ask that he/she remove ALL (even though it may be counter-intuitive) of the exposed outer skull bony table and drill into the marrow cavity in multiple areas in the exposed bone (think whiffle ball appearance when finished).
Post-op, my wound care of choice would be Wound VAC to stimulate granulation tissue from the marrow cavity of the skull. Once that fills in and you have good granulation, then skin graft and be done. If you had poor granulation tissue base, I would take a different approach.
Those are my thoughts. PS: I had a case much like this, except it involved most of the parietal/temporal bone area on the left side of the skull. Failed free flap after radiation. The surgeons flapped over devitalized bone. Didn’t work out too well. We finished with the above approach with a 90% coverage.