They'll still be downloadable and playable in a standalone player.
Also it would technically be possible for someone to write a WebAssembly flash player. Although I don't know if anyone will feel particularly motivated to.
It's always been possible to have free flash players. Gnash is one example. But they've never been feature complete or particularly fast. Maybe if Adobe opened their player things would improve.
The advantage now that flash is no longer being developed is that a player could concentrate on supporting the features used by the most popular content. Like dosbox it might not perfectly replicate the environment (at least to start with) but it could run the games everybody wants.
But that's hardly unique to Adobe. Any document format that allows (arbitrary) other things to be embedded is subject to that. A Word document with other things embedded in it is no different. (Just like correctly rendering or editing an OpenDocument file would require you to implement half of SVG and MathML – while they're open specifications it doesn't necessarily mean you have an implementation at hand you can use.)