That one trick pony is going to be minting cash for the next 20 years at least, just like the Mac has been for the past 40 years.
I remember those failed attempts to rejuvenate the Mac OS and not having any significant Macs sales on my country besides a single importer company on the capital.
Before the Jobs/Cook era, Apple used to have terrible inventory management, that isn't a problem any longer.
Apple used to be extremely dependent on third-party distributors, they now are one of the most profitable retailers in the world, they also have built wide distribution networks far beyond "computer stores"
Back then, Apple had burned through most of the company profits, Jobs and Cook built a tidy trust fund worth approximately $250 billion cash-on-hand
Apple is in a far better position now to handle a debacle or stagnation, assuming one was to happen.
but yes, I do agree that innovations on the scale of GUI desktops and touchscreen pocketable computers take place once every several decades. Interesting that the same company was largely responsible for bringing both of those to market, though...