Every student with a 504 Plan has a case manager. It is required. Look on your 504 form…that person should be clearly listed on the form.
If you have a 504, you no longer need a health plan assuming the 504 addresses the necessary health related accommodations for your kiddo.
The school absolutely should be working with you to help your son graduate.
I think you need to talk to your medical professionals about this as well. Healing from a TBI is a process…and you really can’t push it. It just might be that advanced courses are not in the cards NOW.
Your son’s health is far more important than completing any advanced level courses.