Given your years of service, you have the right to an administrative hearing to determine if you should be discharged and, if so, what type of discharge you can get. Without more facts it is impossible to give odds as to whether you will be retained. Even then, it is impossible to predict what a board of officers will do. Your best bet is to put forth the best defense you can. You will be provided a TDS attorney to represent you and you can retain civilian counsel as well. If you would like...
This isn't a military law question (which deal with courts-martial and the like) so you might want to post in the consumer law section. My recommendation is that he see the Legal Assistance Officer where he is stationed. She can't sell the car because the title is in his name (I assume.) But I don't know if there is any way to require her to ship it over. You also might want to consult an attorney in Washington who handles consumer matters.
There are undoubtedly more issues here than meet the eye. My guess is that the AF is saying that she failed to disclose a pre-existing illness, but that is a guess. She will be provided an AF JAG attorney to assist, and she can always retain civilian counsel on her own. The AF doesn't need much to kick someone out in an ELS status, but she should still speak to an attorney to review all the documentation.
It is up to your command, but in my experience you will get an Under Other Than Honorable Conditions Discharge. If so, they will serve you with a notice to separate you, and you will have the opportunity to request a hearing before a Board of Officers. You would be smart to speak to an attorney about your options, including turning yourself in, as you are now AWOL.
I don't mean to scare you, but this is a serious matter. It is up to his command to determine what is going to happen to him, whether it be a discharge or a court-martial. He needs to have an attorney now. You should call the Trial Defense Service at Fort Benning or contact a military law attorney to assist.
This is too serious of a matter to be resolved in this limited forum. Go to base legal or contact a military law attorney from this site and get fact specific advice. Do NOT speak to anyone else until you have done so.