The simple answer is that atproto works like the web & search engines, where the apps aggregate from the distributed accounts. So the proper analogy here would be like yahoo going down in 1999.
Does Google Reader help you make sense of it? It’s more like each app is like its own Google Reader. And indeed you were able to access the same posts via other apps at that time of outage.
Not the original poster but I do have some ideas. Official Bluesky clients could randomly/round-robin access 3-4 different appview servers run by different organizations instead of one centralized server. Likewise there could be 3-4 relays instead of one. Upgrades could roll across the servers so they don't all get hit by bugs immediately.
Google and MSN Search were already available at this time. Also websites used to publish webrings and there was IRC and forums to ask people about things.