In principle, all databases on the server are encrypted with the corresponding password of the super administrator.
Databases that are actively connected to the server at the time the admins password is changed receive this change at the same time - regardless of whether they are actively used databases or databases of employees who have already left the company.
Older backup files that are still encrypted with the old admin password, i.e. before it was changed, can then no longer be opened in this case, unless the old admin password is still known. In this case you could open it directly via the client (not via the server) and use the old admin password for authentication.