The answer to this is going to depend on what kind of membership these former employees had and how it was being paid for. If they had Creative Cloud individual memberships associated with a company email address these memberships most likely will need to be cancelled and a new ones created for the new employees email addresses. If they were assigned a generic company email only used for Creative Cloud it might be possible to just change the password. You should be able to open the Creative Cloud app and click on their avatar in the top right corner to see what Adobe ID is being used. If they were using a Creative Cloud for Teams type membership an administrator for the team should be able to revoke the license from these former employee email addresses and reassign it to a new employee within the Admin console (all from the company side without Adobe involvement). So as I mentioned, it really depends on the type of membership(s) used. If you're unsure of the type of membership they had contacting support as John mentions would be the best next step.