I think that Eggy went wrong in thinking that Mesaana was of those that disappeared from the tower. It is extremely like that when she re-oathed the tower, she did it the same way as in the Rebel Tower. Made every one re-oath and say whether they were black ajah or not (or darkfriend or not). If she did the same in the tower, then it is likely that Mesaana is still in the Tower. Since she is forsaken, she is NOT Black Ajah nor a Darkfriend, she would be able to truthfully say no. So I believe that she is currently bound with the three oaths and in the tower. Eventually she will get ahold of an oath rod or have the DO break the oaths on her.

Unless I missed something when I read it the first time. Going through it again...