Flash isn't going anywhere just yet, I don't think. HTML5 adoption seems a bit dead in the water at this point - some sites have offered the option, very few have converted altogether, and some (like
The Escapist) have made the aggravating choice to make HTML5 content a
premium thing, missing the point entirely. Flash has its problems, to be sure, but it's also got sixteen years of accumulated content and support, and that doesn't just change overnight the moment someone comes out with a new standard.
And HTML5 is not without its problems, either: for one thing, it depends entirely on your browser having a good Javascript engine; not all HTML5-capable browsers do, and for some of us who live on lower-end equipment, upgrading to a flashy new browser that eats memory like popcorn and enables all kinds of annoying new tricks by bad Web designers to impair usability, all for the sake of enjoying replications of functionality Flash already provides, is not an option. It also suffers from being designed especially for streaming content and "web apps," and thus it doesn't (to my knowledge) have a container format like Flash does. There's no equivalent of an SWF that you can store a complete cartoon or game in and upload to Newgrounds; you'd need to have the whole mess of resource files uploaded in their proper hierarchy. Pain. In. The. Ass.
I have never once seen Silverlight on any site other than Microsoft's.