Is there a way for the admin to be notified when a contact is not sent an email through journey builder? The contact is not sent the email because of some interaction within the journey but for some reason (maybe error) MC doesn't send the email.
One way would be to setup a send log for these emails.
You could then create a verification activity in automation studio to send an alert email when this send log (data extension) has a certain number of records.
You could create a SQL activity beforehand to copy only certain types of records from the send log to a different data extension that you then run the verification activity on as well if you wanted to be more specific.