And what about all the games from 15-20 years ago, or all the "explanatory" pages (e.g., visualizing different types of balanced binary search trees) that used Java applets? This has been done before, and not that long ago. And just like with DOS or NES games, people will build emulators that work well enough and that will suffice for enjoying historical content.

Actually, the really annoying stuff isn't Flash, it's Shockwave. The format's not been reverse-engineered, and it's hard-to-impossible to find a working plugin for it that seems to play some of those old Shockwave games.