Considering the distributed nature of the fediverse, the only way I could imagine the entire thing going down is either a botched update that everyone somehow manages to install at once, or a very sophisticated distributed attack.
The latter would be the most realistic as someone could find a way to poison the ActivityPub protocol or there’s a bug in it and then a message would go to all servers simultaneously.
Considering the distributed nature of the fediverse, the only way I could imagine the entire thing going down is either a botched update that everyone somehow manages to install at once, or a very sophisticated distributed attack.
The latter would be the most realistic as someone could find a way to poison the ActivityPub protocol or there’s a bug in it and then a message would go to all servers simultaneously.