Yes, currently we don't have a way to automatically delete rooms (but it's in my todo list )
So, there are actually two way to manage room cleaning:
1) as Nigel says, keep track of your rooms and run a "cleanup" task once in a while (or just reuse your already existing rooms).
The server integration modules provide a getRoomInfo method that will return an error "not-active" if the room is not currently running.
2) You can also "listen" to room activity using the server-to-server notification mechanism. You can "subscribe" to room events (start, stop) and you can delete the room when you receive the room end message.
My suggestion is: if you are using / are thinking of using the notification mechanism for other purposes, hook the room notification in there.
If you don't think you need to use the notification mechanism for other purposes, have a cleanup process doing the "dirty work" and remove it when we add support for auto-delete rooms.