Yes if client crashes server keeps you on usually some minutes as it might be an short internet issue and getting kicked from groups is not fun either. Now raterly have long loading screens outside of weird bugs.There isn't really a way provided by the game. Usually just using Alt + F4 (or bringing up the Task Manager and shutting down the game) should work, but in some cases the server might still recognize you as being logged in, and you might have trouble re-entering. Normally, this fixes itself after several minutes, when the servers kick you for inactivity.
Yes, displaying a screen that takes an excessively long time to expire, and providing no way to exit from the screen, is just bad software design.