PC computers were already replaced for different use cases so yes, the market shrunk, but they will stay relevant for many others for a long time. Simple tasks can easily be achieved with super convenient rectangles that are effectively computers with different input methods, but they just won’t cut it for anything more complex like 3D modeling, CAD, video editing etc. 30 years ago it was impressive when PCs could hold a large collection of digital music with instantaneous access to all of it. Now it’s just plain irrelevant, as basically all music known to human can be accessed from anywhere with just a handy rectangle. But then even relatively simple tasks like doing taxes is a daunting task on a smartphone, and only a tiny bit more convenient on a tablet.
Of course at some point computers with completely different input and output methods can put all we know today into obsolescence, but I think we’re not even close. Some may say that VR headsets will be the thing, but personally I don’t believe so. While having virtual 3D viewport is fun and games, people seem to ignore what it takes away. Simple things like being able to see the same thing on a screen by multiple people without some video sinks between headsets or ability to interact with things without having to wear helmet or putting anything on (however lightweight it is), would be gone. Don’t get me wrong, they can certainly have their place and things they’re really good or the best at, but it’s just not going to easily replace more traditional input methods. More likely something like holographic displays paired with motion sensors recognizing body movement or some shit