Silverlight was released in 2007 and as rumored lets say Windows 8 probably comes around next year or so - it still managed to provide an alternative to flash for all these years (at least for certain kinds of RIA). If HTML5 becomes a standard, isn't that a good thing that Microsoft is supporting it completely?

Besides that, folks can continue to leverage their XAML (for UI) and C#/VB skills for building even new Metro style apps.