The government won at trial, defended the win on appeal, and lost. There is no “appeal” from that. The decision of the court of appeals typically is the final word. The only avenues are petitions for discretionary review, reserved for special cases: rehearing (asking the appeals court to change its mind), or Supreme Court review. Such review is rarely granted (a few percent of cases), and generally only for a question of exceptional importance to the law, or where different courts of appeals reach conflicting decisions. Neither was true here.
And Congress has abandoned the fiduciary rule by deciding not to pass a new bill that would be acceptable to the courts.