The price of computation continues to drop at an exponential rate. Most people who buy Apple don’t use them for research or work which is computationally expensive. The typical Apple user browses facebook and checks their email. It won’t be long before these users figure out that they don’t need to spend $2000 on a laptop to be able to do this.
Apple will still be around to make quality batteries and good displays (that is, buy them from other companies and stamp their logo on them) because those components’ prices don’t drop exponentially. It won’t be very profitable. The $700B empire will shrink dramatically. Apple will still have a great image (that is, to those who know little about computing) and they will continue to leverage it.