If you had gone to law school, you would know that mere promises are NOT enforceable. And even if there was more than a promise, most statutes of limitation would have run in the past 12 years. And he clearly can disinherit a child, and you are not entitled to anything if he has a properly prepared Will doing so.
BUT may I ask you something doctor? The guy is still YOUR FATHER. He is dying. You had a realtionship until the falling out.
What kind of human being are you? -- What kind of daughter or son? -- What horrible thing did he do to make you not want to try to have a rapproachment, if not make amends at a time like this? This is not a question of your saying you are sorry or his saying he is sorry. This is a matter of letting bygones be bygonesand saying goodbye.
I have seen far too many people destroy themselves and their families over relatively petty things. And I have seen some people wise enough to put things in perspective and take advantage of the chance you have now to set things right.
Think too of the imact your actions will have on your relationship with other family members long term, and on your own family. This is NOT about money. This is about life, and it seems you may have missed those classes in medical school. (They didn't teach them in law school either, but I learned them the hard way.)
This is your last chance. Don't blow it. And may I also urge you to consult with a fellow MD -- a psychiatrist -- to help you sort this out now. My guess is that you have a great deal of residual anger within you based on your focus on the money. Money is no substitute for the relationship you lack. I assure you that the small psychiatrist bill now will save you and others in your family much larger ones later and the saving will far exceed the interest on the loans.