As long as the Desktop exists, some version of WPF will, but you'll see some convergence between WinRT and WPF in the future, so it may not be called "WPF" anymore.
The bigger question is what plans Microsoft has with the Desktop. They've said it won't go away; well, okay, but the question is where its going.
I think the plans for the desktop will be based primarily on the acceptance (or lack thereof) of the Windows 8 Store Apps and the "New Windows" environment. The desktop story makes a nice "Plan B".