Have you ever heard of something like this before?

CANCELLED: Due to the resignation and absence of our track manager, the call has been made to cancel today’s Muscle Car event. We apologize for any inconvenience.

Our team here at Rock Falls raceway are very sorry for this unforeseen circumstance. We are working diligently to fill this position and will make sure continue to offer a great experience here at The Rock. We have many exciting racing events coming up for the season and cannot wait for you to join us soon!! Thank you for your patience and understanding.

Wouldn't a track have a second in command to proceed?

Sounds like a short notice / no notice bail out by the track mgr. You would think they would have a backup, but based on the wording of that announcement, ("Today's Event"), it was last minute. Maybe the backup had prior plans, like a wedding to attend, etc.
Also, if it is a smaller track, they often have very few staff. One such track I used to race at had a manager, (who also worked tech cards and the lanes), an announcer (who also worked cash box, buybacks and payouts), one assistant in the tower to enter dial-in's and timing system, a starter, a water box guy, slip shack girl and an entry gate girl. That was it. 7 people. They could not function if any of them was missing.
(Safety crew/ambulance was contracted, same with concession stand and fuel shack).

When they hired that track manager, it was only a matter of time before it ended badly. Thankfully it didn’t take very long.

It is unfortunate that they weren’t that direction with management right at the time they made huge facility improvements. Hopefully the next manager can right the ship.