I don't think one can say that a patient had lost their autonomy. I'm not sure what basis one could use to say that.
On the other hand, I'd like to repeat the words used by Dr. Marcel Boisvert, a geriatrician and a compassionate doctor, who said that even if someone very old tells us that they no longer want to be a burden to their family, what's pathological about saying that?
It could very well be an altruistic, completely acceptable, and very interesting reaction. Of course, it's important to take into account the fact that such patients are treated over a very lengthy period. You don't decide from one day to the next when you get up in the morning that you're going to make an advance request for medical assistance in dying.
I trust that answers your question.