There are a couple of options available which would bulk deactivate users in your instance.
If you are wanting users deactivated after a specific period of time you might find the user decay task helpful. For more information on this task check out - Users mysteriously being disabled? It may be the User Decay Task
Or if you are syncing your users via an external management system the "Disable federated user accounts not found in the directory" option might work for you - Synchronizing LDAP Users
Lastly, if you are interested in developing a task utilizing the API endpoints I would recommend checking out the Re: Ban and deactivate user by API discussion found in the Developer space for more information.