You should definitely not see any alarms related to robots when you have a hub failure (or lose connectivity) to the hub.
The alarms you would see when a hub goes down or loses connectivity depend on how the communication with the hub is configured. Usually you would see alarms for tunnels and/or queues. A tunnel disconnect should result in alarm on both hubs depending on the configuration. A queue failure probably only generates alarms for get/attach queues but not post queues.