What would happen if kbin's admin (ernest), or any other admin of a server( by that I mean Mastodon, Lemmy, not an instance of kbin) one day decided he's going to pull a spez?

For kbin in particular, what would happen to an instance's Magazines(subreddits), the communities would just go poof?

I'm a rat who left the sinking ship that is reddit and I want to better understand how the whole fediverse thing works. I get that "everyone can host their own instances and access the federated fediverse servers/instances", but if a particular large one has gained traction and would one day implode, is there any way to prevent/mitigate it?