I don’t, but I’m fairly sure that they’re alive.
When someone has advanced alzheimers, his/her body is there, s/he looks like the person you’ve known and loved, but their mind is not there. None of it. They don’t know you. She will look blankly at you as if she’s never seen you in her life. She doesn’t know why you’re even there. It’s gut-wrenchingly painful. In many ways it’s worse than the physical dying of your loved ones. No one who’s been thru that would refer to it as “very much alive.”