One notable major site which uses Flash and which almost guarantees that Flash will not die out any time soon is Youtube.
I'd not ride much money on that bet if I were you.
Netflix is ditching SIlverlight for HTML5 video streaming -- If you visit Netflix with the IE 11 beta, it comes down over HTML5 today even. Then, you have the fact that Youtube is owned by Google, and Google are huge proponents of HTML5 and their VP8 codec, and it would appear pretty clear that they'll want to ditch flash ASAP. It may not be ready for adoption today, but Google is biding its time I'm sure. Once its feasible, flash will disappear from youtube in the blink of an eye. That's where my money is, anyhow. I think we're talking months, not years.
Google is working on it, you can use youtube without flash today if you want.
Adobe is working on it aswell, the latest version of Flash professional can export animations to HTML5 and i wouldn't be surprised if future versions will be able to export interactive content (scripts etc) as well.