That's a rather naive way of looking at it. The name - Flash Player - is deceptive. Player is what users see and what it appears to be doing, but in reality it is much more than that. It is a content delivery system, and the Player is an essential part of it that is expected to play by the rules - DRM, collaborative p2p delivery, licensing, etc. 10% (maybe) of the player is about playback, the rest is what users don't really see, but what is of a huge value to Adobe. Guess what will be stripped off the second the player open sourced? Why would Adobe want that.
For everyone I know Flash amounts to YouTube, Ustream, some other video sites, and some web games.
Streaming video will work just fine with HTML5 or just an old fashioned browser video plugin. A lot of the Flash web games will be missed, but my sense is that the vast majority of those people are using Windows and Mac.
The day is coming when very few new projects will be started in Flash and it will go the way of Silverlight.