Most homes still need the ability to write and print a letter, print a coupon out, etc.
None of which needs a new PC. Sure, there will still be a market for PC to replace broken, unrepairable models, but I stand by my assertion. You'll still get PCs, but they'll be niche.
A similar story befell thermionic valves - they were essentially a stopgap (for different reasons) until transistors came along. You can still get valves - indeed they are essential in some high-power applications. But they're niche.
VHS was a stopgap until we had DVDs. DVDs themselves were a stopgap until streaming media arrived.
In all my 30 years computing, I have only bought 2 new computers. An Amstrad 1512 (which I upgraded to a 1640), and a Memorex-Telex PC in 1992. All the other computers I have owned have been second hand, and/or acquired (legally) from work. In all that time, I have never felt underpowered, or in need of something newer.
Currently the Page household runs on 2 2008 Dell boxes (one for wifey, one for sprog) that I acquired when my office closed in 2010. Running Windows 7, there's no reason why they shouldn't last another 5 years .....