Since he can't prove what happened, it appears to the world that he made a massive mistake in Mesa Verde. In the real world that's a potential claim, and may trigger an obligation to notify the carrier under a professional liability policy regardless of whether they sue him. By not reporting it to the carrier, Chuck/HHM breached their obligations under the policy. Since Jimmy told them he had a breakdown on the record at the hearing, they have even more reason to look into that issue, and they probably already have grounds to drop him.
Mesa Verde probably couldn't win a malpractice action since they weren't actually damaged, but the insurer dropping Chuck would be a major deal. Other insurers may not touch him, and no way HHM could let him keep working without him being insured. Jimmy may have ended Chuck's career with that move.