Is there legal precedence for a doctor to notify a patient of a life threatening condition?

Mom had occluded arteries that prevented wound healing. She developed a horrendous wound that ultimately caused her death. These wounds were a death sentence since removal of the affected limb would have killed her. It is possible her stroke was caused by the occlusion. We spent the last two months of her life trying to get her well enough to come home. Had we known of the occlusion we could have helped her die with dignity and without pain. If we had known of it soon enough it is possible she wouldnt have died at all, perhaps the occlusion caused the stroke that started her fatal slide in health. I ask because I need to know if there is a legal precedence for a doctor to notify a patient of a life threatening condition? We not only didn't find out until months after the test, but found out accidentally, and then the doctor wouldnt see her for over a month. Not until i sought a second opinion did he make time for us.