If you are planning a group, you have access to the list of reservations. From this feature you are able to view cancellations.
Here are the steps to view them:
1. Go to the Calendar tab,
2. Select the calendar associated with the event for which you want to view the cancellations.
3. Click on the desired event or group
4. The event window opens with the list of attendees
5. Then click on the Options icon at the top of the booking form
6. And click on the option "Show cancellations".
7. When done, scroll through the participants screen up to the Cancellations section.
8. You are then able to see all the people who canceled for this event / group.