everard, that's not a pleasant thing to happen.
You can of course try to have the feedback removed by getting a CS rep to phone you. You could point out that the entire country is in turmoil with:
a) catastrophic bushfires, and
b) impacted services (including delivery) as a result of people staying home/isolated out of fear of the coronavirus.
Equally point out that since you issued a refund immediately (no escalation with eBay stepping in), and also courteously offered to send a replacement completely free of charge, your actions do not merit the comment that you "ripped them off". I suppose you could make the point that if the buyer had simply given you a negative with the comment "Item never arrived" or "Missing parcel - not happy - will never buy from this seller again", you would simply have copped the negative on the chin. Point out to the rep that "to rip off" is literally saying that you have exploited the buyer and perpetrated a fraud.
It's certainly worth a try.
Otherwise, you could wait for the buyer to respond - or just send a replacement anyway (along with a note saying something like "Replacement item issued free of charge - original item reported as lost in transit), and then, once it's arrived, perhaps contacting the buyer to see whether they would revise feedback. I think that's less satisfactory, though, than if eBay were to remove the feedback, since you actually did nothing wrong and morally you shouldn't have to wear this feedback.
