And what would it be replaced with?
Smaller, portable devices. Why have a desktop tower or console that are relatively fixed in place when you can have a device that you can easily move around and use on the go? Then we can use peripherals through a docking station sort of mechanism, where these devices can be plugged into and used similar to now.
And like Ladios said, we won't necessarily need high end hardware if it's all accessible online and through something like a browser or similar platform.

Computers will exist for QUITE a long time, even if it's the year 4551, computers can just be a holographic image and a floating portable keyboard.
PC, a.k.a. the personal computer, a.k.a. the large tower sitting beside you. Obviously computers are here to stay...
EDIT: Forgot to original quote.