This is the type of border control that zero has in mind. So if doctors don’t want to work for the 0-care program, they could be forced to do so. If regulation stifles profits and forces companies to go offshore, they will be forced to liquidate instead. Good luck on retiring abroad, either there will be an exit tax or it will be verboten.
You could conceivably force me to come to work. There is no way to make me treat patients. Anyone who saw me as a patient at tha t point would not be pleased.