Is he in a state to talk about it? If so, his view must be paramount. If not, and there's no hope of effective recovery (i.e. regaining a worthwhile- to him- life), the main aim must be to allow him to die with dignity and without pain.

Euthanasia is totally justifiable in such a case- my own mother asked about the possibility when she was dying- and that's despite being a devout Catholic. She suffered a few months longer because of the mawkishness of the law.