The joys of hosting! But I beg to differ on your statement that it's too late to appeal to the Resolutions service; I've discovered missing or damaged items that I was able to confidently trace back to prior guests (after receiving verification from the culprits via the Airbnb messaging platform for corroboration) and succesfully received compensation.
I'd initiate a converstion with the guest in question, see if they accept responsibility and proceed from there.
Best of fortune!