I think it depends on what the family wants. We have a girl in our family who has the brain of a one month old baby. I believe she is nine. They don't know if she can hear or see. Her brain is very damaged. But they would never euthanize her. I'm not sure if she is on pain or not. But she does cry when she's hurting. I think if they were completely helpless and in a lot of pain that it could be likened to someone who was living off a ventilator. Sometimes it's best to let them go. But I think that's something only the family can decide.