I'm actually moving this into General Discussion, because the question is more about law and ethics than about medicine or biology.
If the procedure is legal, and the best option available to the patient, and the patient fully understands the risks that they are accepting in the document they sign, then the doctor is fairly well covered. If any of those don't hold up, then the outcome would likely depend on the lawsuit findings and those of the medical board. For example, if there is a much safer procedure that should be tried first, and is the usual standard of care, and the doctor doesn't tell the patient about that option before urging them into something risky, that's a problem. Or, if the patient doesn't fully understand what they are signing (it's not just "consent" but "informed consent" that is required), either because the doctor rushes them into it (often medical decisions need to be made quickly, and you don't have time to consult a lawyer before signing something to receive treatment...it's not quite the same as signing a loan agreement without taking time to think it over) or doesn't adequately answer their questions, or misleads them about what it says, or doesn't explain medical terminology the patient doesn't understand, then all of those things could raise questions about whether the consent given was "informed."