Can touchscreens replace the mouse and keyboard?

No.
Keyboards have not replaced a pen and paper. A mouse and a graphics tablet can be used as pointing devices but they have not replaced ink, brushes pens or different mediums on which you could produce art.

Although I seldom use the trackpad on my laptop, I could see it as a alternate input device to navigate to play with pressure for painting etc.

When it comes to using a mouse, the number of buttons, multi click and precision is something that touch screens have yet to offer, unless of course you are using a stylus.
Touchscreen are now "the rage" of consumer electronics. A sleek device which has a featureless interface is less obtrusive and feel futuristic by the lack specialized functions.

A touch screen's life may be longer than a keyboard, but consumer culture does not want use to use a computer for more than 5-6 years, so durability can barely be an argument. Who you do know still uses an iPod? It can take less than 3 years for any kind of technology to become obsolete.