Can you talk with your retiring neurologist to see if anything can be worked out?

Our first neuro "retired" because he was getting up there, but also he was sick to death of the insurance paperwork, reimbursement backlog, etc. and etc. ...BUT he advised us that he would, for, I think it was, $200/hour cash (this was back around 2006 or so) still see us, either at our home, his home, anywhere we wanted. It was incredible, and probably what medical care used to be like before health insurance came along. Your neuro may be willing to do something similar, although with COVID maybe you all can skype or video conference.

One thing that came to mind is that I don't think that a doctor/practice can just "abandon" you like this, leaving you high and dry with regard to meds you have been taking for years. You might want to look into whether your state has laws about patient abandonment and if so, whether might help you.

It's so hard to hear about things like this, I hope that you are able to get the care and medicines that you need