For some you don't need them, but for some they are a hard requirement. It means they aren't going to be replaced by tablets. Tablets can take some percentage of activities that used to be done on regular computers - that's true. But not all by any means. Therefore talks about "killing" - are not to the point. When some revolution in the interfaces will happen, and new methods will replace keyboards mouses and wide screens - then one can say the classic PC is obsolete. But that time is not here yet.
No, this can't replace keyboards and wide screens because of incomparable productivity. More like holographic screens and input devices which can take a size of a big monitor (or bigger) and offer convenient interaction methods, while not taking really any space.
