Aside from the fact that people have been prophesying the downfall of Apple for decades, I think it's outrageously naive to imagine that Apple isn't aware of the succession issue. I doubt there's an employee there, including Cook, who doesn't understand the need for a new visionary to move the company forward when Cook leaves. And Cook isn't particularly young at this point, so I'd imagine a transition isn't that far off.

Though I generally agree that Jobs may have made the company too dependent on his vision, what he also managed to do was to instil that vision in the company culture. So I believe the kind of thinking that made Jobs a great CEO is alive and well in a lot of employees, from the top of the company to the bottom. I'd say there are probably a number of possible successors working there right now, though we may not know their names.