Just popping in to clarify @Paul-Winterhalder 's comment about catching the ROOM_ASSIGNED event...

That's actually not the event that should be listened for. That event is only sent if the lobby type has been configured with an associated server type and we've made a request to launch a server instance.

If no server type has been associated with the lobby type, the developer should listen and react to the STARTING event. That will be the event sent out just prior to the lobby being disbanded (assuming "Disband on start" has been selected).