What avenue does a plaintiff has to pursue a claim against a defendant for breach of contract?

A plaintiff sues a defendant. Defendant moves to dismiss. While the motion is pending in the underlying suit, Plaintiff reaches a settlement with defendant in the underlying suit. Neither party alerted the court of the settlement and the court grants defendant's motion and dismisses the underlying suit with prejudice. Plaintiff files a series of post judgment motions to vacate the judgment in the underlying case arguing that the parties had settled the case before the court ruled. Defendants opposed the motion and the court ultimately denies the motion without opinion. Plaintiff sues defendant in state court for breach and the court rules that the denial of the post-judgment motion bar the suit under res judicata. What other avenues does the plaintiff have under these facts.