I get your point. With this you get a single point of failure again (basically ROS1)… If the server is missing the whole system would go bonkers…
I believe, that the (main) server from the DDS Discovery would need to be always inside the robot. So you still have an autonomous “basic” robot that can be extended with multiple resources but maintain integrity during offline phases…
You would then need a clever discovery algorithm that matches/combines these resources… which brings us back to multicast… damn… 
Maybe @Jaime_Martin_Losa or one of his colleagues from eProsima has a smart idea regarding this?