"Physicians have a professional obligation to preserve and advance the health of their patients. Assuming arguendo that the statute should be read as requiring a judgment by the physician that without an abortion the patient will die, the statute conflicts with the physician’s obligation because it commands him to ignore all the health interests of his patient with respect to termination of pregnancy unless he can predict that she will die without an abortion. Moreover, the statute does not tell the doctor what factors he may properly consider in making this prediction; nor how certain his prediction must be before he may decide to terminate his patient’s pregnancy; nor how soon she must die if she does not have an abortion."