This is a very difficult question to answer and I think it will come under Medical Ethics. Usually, if a patient had a Do Not Resuscitate (DNR) order, where he/she wanted the plugs to be pulled in this situation, then the family and the doctors should do so. However, sometimes there is a dispute between families and the families do not want to pull the plug.
In this case that you have mentioned, I think if the patient had a DNR then definitely I would pull the plug as soon as I found out about the loved one. If he did not then I would wait until the rest of the family came in and discussed it. Hopefully we could all come to an agreement and pull the plug sooner than later to avoid too much pain.