I think its too soon to push the "panic" button.
Silverlight is going no where ! I believe the native apps in Windows 8 will be possible through Silverlight (the one similar to Windows Phone 7) and XNA.
The Silverlight for WP7 supports a native install & launch, touch-support with more awesome features like Metro UI theme, Pivot View etc., Given that XAML is very powerful and the time developers invested (in learning Binding, Dependency Property, Styles, Templates, Routing etc.,)will not go in vain. "It may just get better" !
But I am still not sure about WPF, anyway as most of its features are already getting into Silverlight, it won't be the end-of-the-road for WPF developers.
Would only take one simple post from Microsoft to squash our worries.
One thing that was said during the D9 show and tell, when pushed about the lack of change in the office Apps, the lady said "we're not the office team", I didn't take that as a good sign. Shouldn't all teams be on the same page when it comes to Windows?