The files aren’t saved locally. The RotMG developer has their own servers which contain all the account information and that information is site-locked. Go to the game page and in the infobox you (should) see a “Report a bug” link. Click that and fill out the report accordingly. If you don’t get a response within a reasonable time frame (3-4 days) then you can contact the developer directly by clicking their name and sending them a private message from their profile.
The developer has no obligation to transfer your account and they might not even be able to.