According to my view, I feel that both of them will go hand in hand. Right now it is very difficult to say that the Tablets will rule over the Desktop PC or Laptop. The reason behind this is the cost of Tablet PC and limitations with regard to applications running on it. The speed at which the applications run on a Desktop PC and Laptop enables the user to multitask at greater speeds. Where as the tablet PC are not that much faster and they will always have some limitations on them according to its size and the number of applications running on it.
But yes the Tablet PC will be a first option for all the users who use basic functionalities like MS Word, Surf Internet and play Games which don't need require higher RAM specifications.
So there are two categories and hence, Tablet PC and Desktop PC or Laptop will always go hand in hand.
Have a nice day.