Recovering Save Files for Deleted Games
The only way to recover save files for deleted games is to use the browser's console. This is useful for testing or transfering from a deleted version of a game to a non-delete one.
One way to do this is to your browser's console and enter this (pastebin example is used).
window.localStorage.getItem("http://pastebin.com/raw.php?i=old paste id")
The output can be copied to a text file and then can be used in a different version of the game.
Another way to do this is the use IGM's own console functions. This is more complex, but you can read about them in this guide by ScrambledRubiks.
Shoutouts to Lookas for making the community aware of this.