Crap. I'm sorry, Flipside. That is a very cruel disease. My grandfather eventually died of it. If it is any consolation, in the case of my grandfather at least, he lived a long time (over a decade) after we confirmed something was wrong. It was only in the last year or so that communication became very difficult. And even then, his mind was completely intact.
I remember, I was at his house with my family. I was helping trying to help my little brother out with some calculus that was kicking his butt. Integration by parts, I think. Papa could hardly walk at this point, but he comes up to see what we're talking about. I was having trouble remembering something. He brightens up, "Oh, I remember that. You just..." And there he was. He'd been retired for goodness knows how long, his body was wrecked by Parkinson's, and he just whipped out integration by parts with all the missing bits I was struggling to remember, just like that. Brother's jaw and mine hit the floor simultaneously. I mean, you could hardly understand the words he was saying, but it just struck me like a knee to the head: he's still in there. The shell of a body he lived in was breaking down, but Papa's mind was still sharp as a razor. All the way to the end.
It's a ****ty comfort, that at least your mind is still there even as your body control goes, but it was a comfort to me.
Treatments do keep getting better, too. Maybe there will be a cure soon enough to help your friend. Regardless, my heart goes out to you and him and his family.
