Sometimes there is a fair use exception for using characters of others. Whether this applies to you or not depends a lot on the opera itself: its content and message. This is a situation where you probably need an attorney to review the details and issue a formal opinion for your circumstances. If you sell it without that opinion and the other company gets sued, you might be liable for their legal expenses plus any damages. Alternatively, you can sign an agreement with the company that specifically puts all liability on their head.
Answered on Aug 27th, 2012 at 4:27 PM