Despite their political leanings, I believe this court will attempt to avoid making a decision which would set a bad precedent for the DC Circuit. I expect a decision holding that since Sullivan has become a party to the case, he must recuse and a new judge be assigned. The mandamus order to Sullivan will not be binding on the new judge who will be instructed to dispose of the DOJ request to dismiss in line with existing Circuit president.
Correction: Circuit president should be Circuit Precedent
That is what I was thinking too after the order granting the en banc hearing. We will just have to wait and see, although I find these legal battles intriguing.