There's still some pretty fun classic games on Kongregate that I like to go back and play every 3-4 years. What options will we have after 2020?
It's also possible to export any Flash movie as a standalone executable with the Flash runtime baked in. This should be immune to any sort of deprecation. Of course this relies on the developer who holds the original source file to do the exporting.
"Game developers that formerly built games for Flash are quickly switching to HTML and seeing great results. Last week, Kongregate published data about the transition to HTML and the trends in game technologies used on their web gaming platform."
So it looks like stuff is being converted over from flash