Hello Paul,
Welcome to Atlassian Community!
When it comes to the Organization, only the Org admin can add and remove other admins.
Also, we can do that by confirming some information and asking for permission for the main billing contact.
With that said, it's necessary to create a ticket with our support, since we need to share private information and involve other people.
As you are a site admin you can create a ticket. Please, go to https://support.atlassian.com/contact/ and create a ticket for "Technical issues and bugs". Since the ticket is private, you can already mention in the description the name of the person who left.
Regards,
Angélica
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.