There is no chance of PCs dying off anytime soon. But sales are going into a long term decline because people are choosing to buy a new tablet rather than a new PC, and just holding onto their aging core2s on Win7 or whatever. The margins and the growth that were there are no longer there and may never recover to their former level. Even before the iPad came along, it was clear with the first iPhone that there was a serious threat to the PC, because if you can have a full browser in your pocket that's immediately challenged a large chunk of your PC usage.
But I pity the man who tries to replace his PC with an iPad.