We just added a new notification for system admins. It is an email that is sent to each user with Admin role whenever someone completes an online registration and there are no Online Notify Person IDs associated with the registration.

The email very clearly lets you know the purpose of the email. It also contains a link to the Help article about the online registration settings (the text 'see documentation' is the link).

Here is an example:

We also have prompts within the Settings themselves. This new email is just an extra fail-safe, as we want to ensure that every registrant receives a confirmation from the appropriate person.