Steve Jobs described PCs as being like pickup trucks, and he described post-PC devices as being like all the other vehicles people use, from bicycles to SUVs. None of those made the pickup truck go away, and for that matter there is a sizeable market of people who take pride in driving a pickup truck even though they never haul anything bigger or dirtier than a chest of drawers in it.
PCs will be the same way. Available and cheap if you need one, and also available for those just like the status symbol of being a touch guy who fdisks and bash scripts and thinks curl beats Firefox.