As a disclaimer I haven't gotten around to doing any of this yet. As was previously stated you will logout automatically when the next character comes in on the same account. The easiest way I thought to get the last character out would be to write a lich script that quits the game after 60 seconds or so in the absence of a command line way to do this. Maybe do it on a character you hardly ever use and have an echo reminding you to kill the script if you are actually playing the character. Can easily add the script to your autostart for whatever character you do last. I don't know the command line options, but maybe someone knows if you can use the command line to autostart a script that doesn't normally run? That would make it even easier and it could have a much shorter delay to quit.