Flash isn't going anywhere IMO.

HTML5 requires Javascript to do "flashy" stuff, performance is crap and there aren't any GUI tools available. Flash can do a lot more complex logic operations than Javascript. HTML5 isn't standardized yet and updates might take years when Adobe can put out updates whenever they want. Flash also works seamlessly with Illustrator, Photoshop and other Adobe Creative Suite apps.

But the key to Flash's success in the future is that HTML5+Javascript doesn't have any DRM support and probably will never have it. It doesn't have a way to restrict the end user's browser from manipulating the code(i.e. to bypass preroll or overlay ads on videos). You can say you hate ads and DRM all you want but that's the only way you'll be able to watch video streams for free in the future unless all the video sites go to subscription only.