UPDATE TO QUENCH YOUR BURNING THIRST FOR FURTHER INFO REGARDING THIS PONY EXPRESS CRISIS
I put in a package trace at USPS. If they can give me solid confirmation that it was delivered to the correct address, then it's out of my hands. I fulfilled my end of the transaction, and I'm not refunding or replacing anything. I have printed proof that the package was mailed, and a case reference number for the trace. I'll still have to eat a negative feedback, I think, but I'm not obligated to pay for something that isn't my fault - and I won't. If they can't find out anything, then I'll send the replacement game. Either way, I think I've gone way above and beyond.