In arbitration. Now he's saying he'll take it to court. Depending on how the arbitration clause was written, he may not find that easy to do. If he does take it to court, well, IANAL, but I doubt he'll find it easy to get the arbitrator's decision overturned.

Past that, he could either refuse to pay, or declare bankruptcy. Both have legal downsides; both also rather strongly damage his public image. (Of course, if he cared about his public image, he would have gotten off this road a long time ago...)