Perhaps you can contact the publisher and explain that the retailer has gone out of business. Maybe, if you are lucky, they can replace the CD for free. Here is a link to the publishers website:
http://www.mycraftivitystore.com/welcomemyc
On the customer service page they have FAQ and do mention you need to make returns to retailer you purchased from but you have extenuating circumstances.
It is worth a shot. The worst that can happen is they will make you purchase a replacement CD but I have to think the cost will be minimal. Don't mention the part about the post because if you do they will tell you to file a claim with the post office for replacement. If you do that you probably won't have your refund for year. If they make you purchase the new CD go ahead and do so then file the claim with the post office.