With the standard freeware edition, they can NOT end the other session other than wait and let it expire. Depending on how they left the station at work behind, the session may even never expire and they will not be able to log in. This 'keep alive' behaviour is a build-in feature of Joomla! 3.
With the PREMIUM and BUSINESS editions of the plug-in, you will be able to override the above standard 'keep alive' behaviour. The plug-in will then end the 'abandoned session' after the website's configured session lifetime has ended. If you would set the lifetime to 30 mins, the session will have expired by the time the user has arrived at home.
With the Business Edition, you can have a link in the website message that allows a forced log-out, but we do not recommend using this option as the default behaviour.
Is it possible to terminate a current session that exists on another computer? e.g. User has logged in at work. Goes home, and has forgotten to log out, and can't log in. Can they end the other session?