One hell of a story and I'm very sorry to hear of your problems. It is great to see the amount of work that you've done to solve the issue. Putting a band aid on it is not a means to an end. Trauma, either head or testicular can impact hormone production. I'm surprised the doc's at the Mayo Clinic feel the need to actually see something on an MRI (pituitary or otherwise) to actually concur.
I've read studies on progesterone combined with Vit D as a possible remedy but can't remember the outcome of the research at the moment. Also, as you are no doubt aware pain meds in higher doses can also impact T levels. So your hormone levels are getting hit from two sides.
Easy to say "If it were me" but, I'd more than likely opt to start with a solid HRT protocol and give that some time on it's own and see how you do. Know that it can take months for the beneficial effects of testosterone replacement to help. It's also important that you have a doctor that understands hormone replacement as some are in the stone ages unfortunately.
This particular forum is really just for introductions but I wanted to respond to you. I will see about getting this moved to the HRT Forum for more responses.
Welcome!