Ideally, everyone who signs up to your events through your Beacon event registration form will end up coming to your event. But, where they can't, here's how to manage the cancellation process.
Delete the Event attendee & Ticket records
If someone isn't going to be attending your event, you should delete both their Event attendee and Ticket records so that they aren't counted towards your limits on any live event registration forms - you don't want them keeping the place of someone else who wants to buy a ticket!
If useful for understanding later why the record was deleted, you can add information in the 'Notes' field of the Ticket.
Keep any Payment records
Since it was still a transaction that happened, you'll likely want to keep the Payment record so that you have that history for your financial reconciliation.