He's likely not dead, just so incapacitated by his dementia that they can't let him out in public without risking someone catching him doing something absurd.

Dementia is a disease that gets worse in waves. You can be lucid one minute then the next become completely unaware of anything, forget who and where you are etc.

They tape him on a green screen when he is doing well, then place him in timely videos to make it seem like he's out and about.