All support to other decentralizers but nothing never goes down.
If tens of servers go down, then some people may start noticing a bit of inconvenience. If hundreds of servers go down, then some people may need to coordinate out of bound on what relays to use, but it still generally speaking works ok.
It's like saying "English never burns". Sure, you can't burn English but you can burn specific books, newspapers and so on.
When I tried it long time ago, the idea was just a transposed Mastodon model that the client would just multi-post to dozen different servers(relays) automatically to be hopeful that the post would be available in at least one shared relays between the user and their followers. That didn't seem to scale well.
The basic idea is that for microblogging use cases users advertise which relays their content is stored on, which clients follow (this implies that there are less-decentralized indexes that hold these pointers, but it does help distribute content to aligned relays instead of blast content everywhere).
Also, relays aside, one key difference vs ActivityPub is that no third party owns your identity, which means you can move from one relay to another freely, which is not true on Mastodon.
I've been wondering if the multi-firehose architecture is really where decentralized censorship resistant microblogging should be the way forward; I remember the Windows Mobile clients for 2ch.net(today 5ch.io) that would scrape thread deltas from bunch of subdomains under it was plenty fast on 128k(advertised) connection to get thousands of posts in late 2000s, and so I think an RSS style of systems getting delta updates from multiple domains could work without having to do the insanity of early Nostr, or massive liabilities for instance operators with Mastodon, especially if those multiple domains could be set up with relative ease.
Yeah, I don't exactly understand why you have to sign up every time to Mastodon servers and server operators to have to be responsible about users. It worked when it was urgently needed, which was brilliant, but the ID system had under baked spots.
> scale well
It is up and it is growing.