It's not true that this is necessarily over. If you think you can prove it, there are grounds for vacating arbitration awards based on a few narrow grounds per the Fed Arb Act (FAA). They are not common but not completely unheard of. According to the FAA:
(a) In any of the following cases the United States court in and for the district wherein the award was made may make an order vacating the award upon the application of any party to the arbitration—
where the award was procured by corruption, fraud, or undue means;
where there was evident partiality or corruption in the arbitrators, or either of them;
where the arbitrators were guilty of misconduct in refusing to postpone the hearing, upon sufficient cause shown, or in refusing to hear evidence pertinent and material to the controversy; or of any other misbehavior by which the rights of any party have been prejudiced; or
where the arbitrators exceeded their powers, or so imperfectly executed them that a mutual, final, and definite award upon the subject matter submitted was not made.
Again hard to do/prove. But if you can make a convincing case of bias, you can at least challenge it in court and may give you a bit of leverage for settlement.