If they can't target some particular group then they just shut down the whole thing. This more highlights the problem of systems with a single point of control.
Multiple providers who federate would still not be enough. With some effort one could block every XMPP server, Jami (or Tor) node out there. You would need something like Briar which does mesh networking via Bluetooth.
With "some effort" you can block anything. Encryption is better than open, federated and encrypted is better than centralized and encrypted, federation over a mesh network is better than just federation.
