Sorry man, that sucks. However, restore the images if you can, they are yours.
You were coerced into destroying images that were your property. Regardless of whether or not photography is allowed on the premises of a private venue, once you have taken images, they are yours, by law. Short of a court order, private parties or law enforcement have no right to force you to destroy images, nor can they confiscate your film/memory cards (unless you're being arrested). Since it's private property, they can ask you to leave, but that's it.
Next time, take a few printouts of this so you know your rights:
The Photographer's Right