Oh man I'm sorry to hear that. I hate to say it but IMO you're going to be better off to cut and run. I don't know about you locality, but in my area variances are few and far between. My family owns a business that is "non-conforming". It's a flower shop in an area of light industrial/office. The business was started in 1948 by my grandfather and has been owned and run by at least one member of the family ever since. In 1976 we had a fire that almost completely put us out of business. We were lucky because we were allowed to rebuild and get back in operation. If there had been any more damage than there was we would have been out of luck. We were able to save just enough of the original structure to let the city allow us to get back up and running.
I would think to grandfather in a business in a non-conforming use it would have to be the same type of business. I doubt that they would allow a business change from one non-conforming to another.
Good luck if you decide to still pursue this location.