Nobody can shut down the fedivers. Thats the whole point of it.

Defederation is the Hammer in the Toolbox of Server Admins/Moderators. With that they can smack every connection between there own server and another, effecticvly ending the communication beetwen users on both servers.

They can still talk to all other severs that are not defederated.

Mastodon has the option to “Silence” or “Limit” servers aswell - that way users can still interact across server but there are some protections enabled(like you have to accept followers from the other server bevor they can see your stuff - and more)

So there are multipile tools to handle Meta.

Little prediction from me, there will be 3 Typs of servers:

Server 1: No Federation with Meta at all - every Meta server is getting defederated
Server 2: Limited federation with Meta
Server 3: Full federation with Meta

all 3 typs will exist and federat with each other.