Yeah this feels like way long shot simply based on his timing being off but I don't know enough about vocal cords to know how far off it is. It's almost like he can't produce the sounds fast enough to keep up with the time but until there's more symptoms of dementia it feels like a reach

"It's clear he isn't concentrating on stage, but we can't be sure if it's because he can't, or just doesn't care to. "

I very much disagree with this, you can tell in his face he knows he's doing a bad job. There's no option now but to keep going. Cancelling the rest will be insurance hell and disappointing what's left. The tour really should not have happened at all.