Although I think any predictions that span five years are stupid to begin with, let’s assume the prediction is correct. Imagine in 2017, the iPhone is no more and Apple is selling precisely 0 of them a year.
Does it matter? Not really. Apple has already moved on to their next $150billion dollar project, the iPad. If, as Strategy Analytics believes, smartphone growth is nearing the end of its life, it affects other manufacturers much more significantly than it does Apple.
Other manufacturers are struggling to maintain profitability today, in the supposed boom of this market. By contrast, if demand for iPhone collapses, Apple is by no means doomed. The Mac business alone would keep them in the Fortune 500, for goodness sake.