I understand your concerns. It's never easy to deal with an upset customer, especially when you've done everything you can to resolve the issue. Have you tried reaching out to the buyer and explaining the situation? It might help if you let them know that your absence was due to a family emergency, and that you are doing everything possible to rectify the situation.
Assuming that you have already processed a refund for the buyer, I would recommend that you politely explain to them that there is no further action required on their part, as they have already received their money back. In most cases, it's simply a matter of miscommunication or misunderstanding between the seller and buyer.
If despite all of this, the buyer continues to bother you with messages, try not to engage in any confrontations or arguments. Instead, keep calm and professional in your responses. You could also consider blocking the buyer from contacting you directly if they become excessively problematic.
As far as feedback goes, it is always possible that this situation could result in a negative review from the buyer. However, as long as you have been transparent throughout the transaction and have done everything by the book in terms of resolving issues, potential future buyers should be able to see this in your seller history. You may also be able to appeal any negative feedback through eBay's customer service team if it was unjustified.
In conclusion, communicating honestly with the buyer and maintaining a professional demeanor will go a long way towards resolving this issue. Keep any documentation related to shipping or refunds so that in case there is an escalation at least you don't get blamed clearly for it being fault by organizing documentation rather than letting one party be heard over another conflicting version of what happened based on memory only.
