The last time a major tech company shifted from its visionary leader to someone else, that company crapped on itself. Who was it? Microsoft. When Bill Gates left and steve ballmer came in, Microsoft's stock lost value, they lost ground everywhere, they came into new markets late, and vista effectively defined the last decade of Microsoft.
apple losing its visionary leader to someone that the leader trusts and is close to him, Tom Cook, may follow the same route. If I was a betting man, I'd say that apple's vision and "innovation" will stagnate. They need major innovations to keep them going.
Although I don't wish the end of people because they lead apple, having said that, the reign of Microsoft may come back this decade!
Hopefully steve jobs gets well though...