I practice in Georgia, but i seriously doubt that the Supreme Court just issued a blanket statement that any time a wheel comes off nobody is at fault. If someone was negligent in putting that wheel on, didn't screw it on, used the wrong size, put on a defective tire, etc. then there are going to be damages to pay.
Maybe your attorney found a case from the Supreme Court that fit the facts of your case and determined there was no cause of action, that's possible.
But attorneys drop cases for all kinds of reasons. Sometimes they find out there is no cause of action, sometimes they discover information the client didnt' tell them about, sometimes they determine it won't be profitable to continue, sometimes the client is a supreme pain in the ass and they decide it's just not worth putting up with for the money. Those things happen.
The good news is there are tons of attorneys out there. If your attorney terminated your relationship, go meet with another one. Get a couple of opinions and pick one you are comfortable with. But don't wait too long. There is a statute of limitations (big words for a time limit) on when your case can be filed. In Georgia on an auto accident case it would be 2 years from the date of the accident.
UM is uninsured or underinsured motorist coverage. That means if someone else does something to cause an accident and they either don't have insurance or they don't have enough insurance to cover it all, then your insurance company will pay for it and then go sue them to get their money back.
Legal disclaimer: Brian Tevis is licensed to practice law in the State of Georgia. All information given is based only on Georgia law and is not directly applicable to any other jurisdictions, states, or districts. This response, or any response, is not legal advice. This response, or any response, does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information. Any state-specific concerns should be directed to an attorney who is licensed to practice law in that respective state.