I am sorry for your loss. My mom died of Alzheimer's as did my uncle so I understand that "Long GoodBye" and how awful it is.
Watching him, knowing that some times he understood while other times he just was in la-la land, it hurt.
No look of recognition in his eyes, just an animal like stare.
My sister was feeding him tonight, we knew it was coming soon, he started breathing real bad, she held his hand, asked him if he wanted my Mom to be there, and he vigorously nodded yes, so, my Mom came, my brother in law started making phone calls to get us there, but I lived too far away.
When My Mom got there, he held her hand and went quietly soon after, just going away, breathing slower and stopping, within a minute or two after she held his hand.
They asked him to hold on for me, but, he couldn't.