You pay me in advance for a product, I owe you that product. Just because you wait some time to come and claim it, does not mean I magically owe you nothing.
My Folks were almost ripped off by a national chain that way, they were a week away from the expiration date.
I don't mind if you want to sell me a gift card with an expiration date plainly stated on the card, AND if I am able to redeem the card for full face value in cash if I do not want or need any of your merchandise.
Anything less is theft.