paying for USPS fault

[zljones]

This has not happened to me yet as a seller, so I am simply asking because I have always wondered what others think about what a policy should be if a seller ships out an item with a tracking number, and scans are shown as moving through sort facilities then the item suddenly falls off the face of the Earth and is never delivered. Let's also say that the seller used the exact correct postage amount, packaged it right, and shipped to the correct address that was provided and did absolutely nothing wrong. Also I am not including situations where there was never a scan to any delivery facilities, in that case a refund I think should be issued, so let's leave that issue out.
Do you think the seller should be responsible to refund the money in this situation, even though it is clearly the post office's fault? Does the seller have a moral obligation to issue a refund even though they are not at fault? Poll attached