Tablets will replace laptops, there's no question of that. Simply because they are laptops with more functionality, at least in the long run. The mouse is awkward with a laptop, and those touch pads are just lame. Tablets will continue to get more powerful and larger, and laptops will continue to disappear, because the touch screen does have value in mobile applications.
However, the desktop is still the best device to compute on, and the mouse and keyboard are still the best interface. I'll be damned if I'm going to keep touching my screen while computing on my desk, as it's awkward and makes my screen dirty. It's also not as efficient.
It kind of reminds me when it was said minicomputers would eliminate mainframes. Laptops would eliminate desktop PCs. Mainframes are around and doing well, minicomputers are extinct. Desktops will be around and doing well 20 years from now, laptops will be extinct.
Although, the distinction between a laptop and a tablet, especially like Surface, are minimal anyway. Essentially, the new tablets will just be a tweaked laptop anyway.