What does the tracking show?
If the buyer opens a case stating that the item has not been received, as long as you can prove delivery was attempted to the address the buyer chose when they checked out, Ebay should close the case in your favour.
The fault here lies with the buyer - they should have checked their own delivery address when they paid.
It is very unlikely that Rm will be able to correctly deliver the parcel or return it to you - locating your parcel would be like trying to find a needle in a haystack
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)