You could use the action em_booking_changed to detect when an event is canceled
add_action('em_booking_status_changed', 'my_booking_status_changed', 10, 2);
function my_booking_status_changed($booking, $assocArr)
...
}
The argument $booking is an object of type EM_Booking and the $assocArr is an associative array with the keys as follows: ‘status’, ’email’ (value can be true or false), ‘ignore_spaces’ (can be true or false).
There’s an action ’em_bookings_deleted’ that gets the following arguments: $result, $booking_ids, $event_ids
There’s an action ’em_bookings_added’ which gets a single argument: $EM_Booking.