As an inexperienced eBayer, and possibly lacking common courtesy as well, he may not realize he should have corresponded with you. I would follow through with tracked delivery of the coin he won, and follow up with him immediately after delivery.
Well, if he refused the first shipment without opening the package, this confirms he's receiving and reading your messages. He's probably waiting for the coin you were supposed to send originally. I'm thinking if he wanted his money back he would of told you. And yes, it's probably a good idea to send an extra something for the inconvenience of having to wait longer. It could save you on feedback. Who knows, it may also get him to buy from you again.
Send him the coin. It's easy to make a mistake on eBay. I've done it as a seller before, usually it's a detail in the listing I forgot to edit out because I use a standard template for many of my listings. When I make a mistake as a seller, I usually throw in a freebie. Doesn't have to be anything big, sometimes it's a heavily circulated Buffalo Nickel or Indian Head Cent. I think my customers appreciate the gesture. Take the long term view...happy buyers are repeat buyers.
Could be he doesn't even have a computer and he was at his Mom's house when he bought the coin from you. Just do your part and everything should work out fine.
+1 (As well as those who have said maybe the buyer either doesn't know how to read messages or hasn't had time - maybe they don't have their settings lined up to notify them via email when they have an eBay message.) I like the idea of documenting what you're doing by sending them a message. This will be helpful in case the wheels fall off the bus later. I also like the idea of a freebie or two.
Well, since the coin was returned he obviously read the email but simply chose not to respond. The seller should immediately send the original coin via priority mail to get it to the buyer as soon as possible. And really, no correspondence is really needed, just send the coin and be done with it. The sellers feedback will more than likely suffer but that's the price for not paying attention. Right?
Yeah, amazingly enough, there are still people who don't understand much of eBay. It's probably a bit of a miracle that they were able to place an order at all.