If it someone who has been seriously training, on a day-to-day basis, I suppose it depends on the person...a 2nd degree black belt obviously won't forget all that they have learned and experienced, no matter what. However, a green belt, (for example, no offense to any green belts here

),who comes to class once a week, and practices even less then that, dosen't care about what they are learning...I've seen plenty walk away, forgetting about everything they have been taught.
To sum it up, if it's someone experienced, who cares alot about the art itself...I think it's possible to walk away, but it would be very hard, despite their reasons.
I know no matter how bad things got as far as politics, etc, got to be, I could leave the perticular dojo if it came to it, but never the art.
Respectfully, kenponochikara