What we know for certain is that Apple can still _execute_ very well and stay competitive in a certain market. The latest offerings of Macs, iPhones and iPads are ample proof of that.
The question which is still unanswered is whether Apple, with Tim Cook and the other leaders, has what it takes to stay innovative. It's too early to tell, and I think it's certainly to early to write a book about it.
Since Tim Cook has gone on record saying that we will wee new product categories within the year, my guess is that we'll know for certain in 2-3 years time.