Went down where? If the Garmin servers are down, nothing goes anywhere. Even device to device traffic goes through the servers.
I don’t know how resilient the Iridium satellite network is. The satellites themselves form a mesh network. They relay messages from satellite to satellite until they reach one that is currently visible to a ground station. Then satellite to ground and onward to Garmin servers. No idea how the “final” satellite knows it’s over a working ground station…
Bottom line is that it has a lot moving parts, some of which are subject to ground power outages.
