Managing forks across organization when staff leave

I wish to understand how to remove all downstream forks once staff leave the company on the Cloud version of Gitlab. I want to understand how Gitlab deals with these issues.

Say I create Group A, and house all my Projects under that. I then grant my fellow staff members access to various Subgroups under Group A. They proceed to fork the Projects under their own name.

At some point, Employee X leaves the company. I then revoke their access to Group A and all Subgroups. My questions are:

  1. How do I then ensure that their personal forks of the Projects they had access to are deleted?
  2. How does the ability to Remove fork relationship affect the ability for me delete their forks?
  3. Is there any way to prevent the Remove fork relationship on forked Projects?

I understand perfectly well that Employee X will have a local copy of the code sitting on their machine. I would still like to understand how Gitlab deals with these permissions issues.

I have seen this asked here How do we delete forks?, but that had no answer.