Answer:
It is the responsibility of the PIC/formation leader to ensure that the proper agency is notified of flight termination.
When a flight is terminated there are many people that need to be told that the flight is canceled. Those at the flight level - pilot, aircraft workers, those working on the ground level for the flight and the travelers. When a flight is canceled everyone needs to make sure they receive the right information as far as why and what changes are going to be made/rescheduled.