It sold on November 13th. The strike started on the 15th. I don't think they would have anything to gain by making a random post if they didn't actually drop it in a mail box or hand it in at the post office.
What I would say to the OP is, it's a tough break. What you have to accept about selling online is that things sometimes go wrong. As far as eBay is concerned, because you did not get a scan they have no way to know that you sent it. Put yourself in both the shoes of eBay an the shoes of the buyer.
If you did in fact send it, what will happen now is that it will start to get scans as it moves through eBay's processing facility, and eventually be delivered to the buyer. You may be able to contact eBay and explain this to them and have them appeal the refund after it is marked as delivered. You also may be able to have the feedback removed. Try contacting the AskeBay account on Twitter (direct message them). Wait until after it is marked as delivered.
While I never get acceptance scans for cheap items because it is not worth waiting in line, the problem is that you didn't get a scan when it was publicized that there could be a strike any day. It's just really bad timing and luck on your part if that is what happened.
The other lesson would be in communication. I don't know if you pre-emptively messaged your buyer - but if you sent them a message right away letting them know it was dropped off at the post office, and if they don't see a scan right away it's because of the strike, they might have been more forgiving and patient. Even if they opened an INR, respectful communication increases the chances that a buyer will make arrangements to retrun the refund or the item when it eventually arrives. eBay does allow sellers and buyers to arrange for the buyer to repay an INR using Paypal or E-Transfer if an item is successfully delivered after a refund.
You could always contact the buyer and let them know that it was in fact sent and since the strike is over they should see progress on the tracking soon. You could instruct them to refuse the package when it arrives, or to accept the package and contact you to arrange to repay the refund. There is nothing obligating them to do either other than their own ethical code, but in experience most people repay INRs when they do arrive. (Some don't, it's the cost of doing business.)
