You are correct in that it is possible to transfer that body of knowledge over to the other gaming industry that is casino machines. Beyond that, here are some other roles that game design skills could transfer to.
Tabletop, board, or card game design. It's still game design, just not in video games.
UX design. Crafting experiences is a useful skill for any user-facing applications. Figuring out what the intended experience should be and adding/modifying/removing elements of the application to improve the user experience is something many game designers can do.
Interior/exterior design. This role is mostly for level designers. Being able to take a space and turn it into a place that makes those who enter it feel a certain way is a valuable skill. Laying out the floorplan for an event, arranging a home or office space to make the environment intuitive to navigate is a big deal. Also, doing architecture for theme parks falls in this category as well.
Simulation/Training/Educational design. There is plenty of crossover with game experiences here, but the goal isn't to get the user to have fun but to train them and teach them stuff. Crafting an experience here involves figuring out how to teach the proper information in an intuitive way.
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