If the customer hasn't contacted you to ask for a refund, then why would you be worried that they are expecting one? It's an unusual case, and I'm glad you are so contientious, but sometimes we make things more stressful for ourselves than we need to. Maybe there was an upheaval in their life and they don't live there anymore. I think it's fine to just keep it and wait, in case you hear from them, then ship it when you do.