Every day is a new day, so I'd not count anyone lost completely beyond repair, even if to an extent everyone has some damage that will never fully be reversible.

That said, it can be a real uphill battle. Especially with head trauma. Sometimes wake up calls come and can actually help though. My brother recently wound up in the hospital after losing over 50 lbs not eating and on the verge of a diabetic coma. He finally let me know he was interested in picking up running after all these years of being a couch potato.

We'll see what sticks. At the end of the day you do have to give people room to make their own decisions, but that doesn't mean you have to completely give up hope.