Using this endpoint is not the only way a webhook can be deleted.
The following reasons can cause webhooks to be deleted.
Deleting a Box application automatically deletes all webhooks associated with
it.
Deleting all active Access Tokens associated with a webhook
automatically deletes the webhook. This includes Developer Tokens and password.
A webhook is automatically deleted if the last successful delivery was
30 days ago and the period between the last successful delivery and
the last trigger date is more than 14 days.
In all of these cases Box sends a webhook payload with the
WEBHOOK.DELETED event name to the notification URL. The body of the payload
includes the following additional information.