If it was a true copyright (one of my favorite designers pursues the less expensive design patents instead), then it is still in effect. A patent would have expired by now. Patents & copyrights are never tied to whether a particular business remains active or not. In fact, it's possible that the owner(s) may have sold their Intellectual Property (patents & copyrights) to another person/entity.
http://www.inventionstatistics.com/P...e_Periods.html