The judge could have questioned the nature of the witnesses called.
Had they been caught, Millicent and Olive could have been sent to juvenile detention or community service for dining and dashing. Freddie would have been held financially responsible as Millicent's legal guardian and it's possible Harper could have faced legal consequences.
The judge could have kicked out Carly and Spencer for interrupting in court although she does so to Spencer when Chuck appears. Although he was escorted out of the courtroom, Spencer could have also been arrested and charged with attempted assault when he tried to reach for Chuck.
Carly could challenge Trina in court as she obtained Carly's signature without consent.
Lewbert could have sued Sam Puckett, too, as she was just as responsible as Carly for any damages done, or sued the entire iCarly team as one party. However, Jennette McCurdy, the actress who portrayed Sam in the original series, refused to return for the revival, so even though she may have been sued, she would not appear in this episode. It is possible he sued her separately before the events of this episode.
Even though they are not listed in Lewbert's lawsuit, Nora Dershlit and Nevel Papperman could have also testified against iCarly for the damages they did to them.