What happens when there is a Motion Calendar Notice of Hearing filed, it gets scheduled by the Court, opposing counsel calls the day before the hearing, an agreement is made between both attorneys to not attend the hearing, a Notice of Cancellation of Hearing is NOT filed and on the day of the hearing both attorneys do not attend?
My guess is that you have a very unhappy judge.
Hearings are frequently canceled and it is common that notice of cancellations are not docketed for a few days because of the lag between the parties the clerks office and the judge. It is also possible that the attorney that scheduled the hearing notified the judicial assistant that the hearing was canceled. Other than that, I can't see a reason why an attorney would risk "standing up" the very person who may be ruling on his next motion.
If the party whose motion it was takes it off calendar (cancels it by giving notice to the court), usually they have to give notice to all of the other parties as well, either orally or in writing, but it's not necssary to file a Noice of Cancellation. The important thing is to give notice so no one shows up for it.
Disclaimer: I'm only licensed in CA. Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.