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.
So-called morality that isn't absolute isn't worth a bucket of warm spit. The act of taking a human life is either morally correct or incorrect, right or wrong, white or black, there are no shades of gray in that act. A person who takes human life will be judged either innocent or guilty by the only judge who can impose a sentence that will last for eternity with no possibility of parole.
There are several legitimate reasons for taking another person's life, self defense, national defense, etc. A disability which makes a person inconvenient to their spouse's future plans isn't one of those reasons.