Wake me up when Microsoft comes up with a tool that allows non-coder graphic designers or animators to create entire apps in Silverlight with the same ease that you can with Flash.
That's the assumption sideline-commenting non-designer coders who aren't in the web or multimedia industry make, like a lot of guys here in Slashdot who do mostly non-frontend stuff. Until then, don't expect Flash to vanish anytime soon.
Same case goes for HTML5. Without proper authoring tools for the non-programmer layman, don't expect any other tech to knock off Flash from its perch. Nothing comes close to the Flash Professional authoring tool's ability for creating vector animations and integrating motion, sound and interactivity with ease today.
Even then, Adobe CTO Kevin Lynch announced that Adobe would be the 1st one to build the same kind of tools for HTML5. In fact, they've already built
HTML5 + CSS3 support for Dreamweaver.
As for video, there's a good reason Flash exploded on the net long before it had the capability to play videos, so don't expect alternative video players to end it either.
Heck, I heard even Blizzard used Flash for certain parts of Starcraft 2's UI. [citation needed]