Let me explain how it works. Each time you make some action in our system (push some button), the current timestamp is stored as "last known action" made by a player. This data is used to evaluate if the player is on-line, off-line, not interested or dead. You don't need to logout to let the system know that you are no longer on-line.
When you don't log out properly, you just loose the option to see new posts/messages correctly. But this really doesn't bother other players.
Session timeout is currently set to 7 days, i.e. if you log in and don't make an action for more then 7 days, the system will make you log in again, if an action is made.