I really don't understand what "WPF is dead" should mean. Silverlight and WPF are basically the same technology (XAML + Code), they just happen to run in different environments. So what the guy probably wanted to say is ".NET desktop apps are dead", but that is clearly not the case.
Regarding Silverlight and HTML5 I happen to agree with http://team.silverlight.net/announcement/the-future-of-silverlight/
Silverlight has it's specific uses, and there it is currently a much better choice than HTML5.