The situation is now resolved.
(Not entirely to my satisfaction, but it's resolved.)
The day before I'd have had to either escalate to a claim or close the dispute, I contacted the seller again and informed him that PayPal had stated very definitely that he could certainly refund me without my closing the dispute - and that this was the proper way to go about it.
(I had rung Paypal just to confirm - in case there really was some reason why the seller would be unable to refund in this instance unless I closed the dispute.)
I said I would accept his offer of 12 euros partial refund, not in that it covered my loss, but that it gave us both a partial degree of satisfaction. For me, it was really a token acknowledgement of responsibility from the seller. I stated that he had to refund me before I would close the dispute, and that I would prefer not to escalate to a claim.
The seller agreed, and sent me 12 euros. (Unfortunately, he didn't seem to follow the link I gave him, which would enable a partial refund - which would mean no fees when I accepted the payment. AAAAgh. He just sent it as a payment rather than partial refund (hence I was charged a fee). A LOT of sellers don't seem to understand how this works!)
I shrugged, and closed the dispute.
I haven't left feedback. If I did, I'd probably give a neutral. Because he did carry through with the partial refund, I consider he kept his end of the bargain and I must deem myself partially satisfied.
Thanks, everyone, for your helpful advice! I made good use of it and refused to close the dispute until being refunded. I truly appreciate all the help you've given.