There is a user idle timer that removes inactive users from user table after 5 minutes (default) of inactivity:
Maximum period after which a client is considered idle if there is no wireless traffic from the client.The timeout period is reset if there is wireless traffic. If there is no wireless traffic in the timeout period, the client is aged out. Once the timeout period has expired, the user is removed. If the keyword seconds is not specified, the value defaults to minutes at the command line
Range: 1 to 255 minutes (30 to 15300seconds)
Default: 5 minutes (300 seconds)
I'm not sure if the associated user will be deauthenticated when they're removed from the user table... Although, as chatty as most devices are these days, I would suspect that if it is not active for 5 minutes, then it probably is not associated to an AP.