It is likely that the court will require that you and he actually attend mediation, possibly on the day of the hearing, before proceeding with the hearing, in the absence of an emergency. If necessary, the judge can make an interim order pending the completion of mediation.
Clearly, by him not showing up for the mandatory class without providing you some kind of notice that he wants to do mediation per the agreement, he is not cooperating with the agreement. I have not seen a court in Orange County (where I practice) refuse to hear a case because mediation (other than through the court when you file an OSC) did not happen. I doubt he will be able to use the agreement as a way to delay things. However, he is delaying things by not attending the mandatory class, Simply go to the OSC, and let the court know what's happening. The court may give him another shot at it, unless he fails to show at the OSC.
As far as saying he didn't get the notice, did someone serve him notice of the OSC? As long as a properly filled out Proof of Service has been filed with the court, he can claim he didn't get notice, but the court will not believe it. If he has retained counsel, he will likely be more cooperative with the process. You may want to consult with and now hire your own attorney.
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