I am investigating what the expected alarms are for the following scenario:
If this hub fails (either the hub element or the entire server):
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.
There are however some bugs (specifically related to failovers and using proxy_mode), that causes "robot inactive" alarms. Problem is that the hubs sometimes gets confused about where the robot should be.