Man has a stroke. Can't swallow, make voluntary movements, or speak. Breathes and regulates blood pressure on his own. Remains in this condition for 13 years, kept alive by care requested by legal guardian. Brain scan shows little or no activity. History of similar cases shows little or no chance of reversal of condition.
Go ahead and riff on your absolute moral principles and their applicability for the doctor and the legal guardian. It will be easy to see why you are not a doctor.