This may prove to be an interesting one but you should be in pretty good shape. Since the watch is being returned to the authenticator they should, according to process, verify the same item is coming back and then return the item to you.
This is where it may get a bit interesting. The policy is not real clear on "return to sender" where the buyer had an incorrect address. In most instances eBay considers and incorrect address the same as delivered and technically you are not required to refund anything to the buyer. There is also the "all sales are final" option/clause that goes with items going through the authentication center but no sure if you had that set in you listing.
While you may not be required to refund the buyer once you have the item back ethically it would be the right thing to do rather than keeping the $3.2K the buyer paid. However, you should deduct all the shipping costs and fees from the refund amount. Just curious have you attempted to contact the buyer? You may also want to contact eBay through the facebook connection as this may be an authenticator issue if the authenticator messed up the shipping to the buyer.
Let us know how this comes out it is an unique situation.
