Migrating to a new AD, what to do with LDAP connection


I am migrating to a new AD-server and have a GitLab server on a different machine. GitLab is authenticated via LDAP to the AD-server and all users have been created by that connection.

Our old AD is not working properly so I am closing it down. What will happen to my GitLab when suddenly people try to log in with the same name but the old LDAP connections is no longer available.

Best case scenario is that I can shut the LDAP connection off and keep the users in GitLab. Is this possible?