I have a return stuck in-transit from buyer. When can I end the return attempt?

[jj4everjj]

In short we had a buyer return an item on Nov. 6th.  We provided priority mail label 2-3 day delivery, tracking, and insurance.  The returned package is still stuck in-transit since the 6th.  2 seperate sorting facilities have held on to it for 4 days each.  The latest isn't releasing it still today.  When as a seller are we allowed to stop the impossible return so our funds are released that are on hold?  Is there a time frame the buyer has to go by after they return ship the item?  Please help!  I dont want to wait forever for this package that seems like it is never going to make it back!!!!