I’m busy right now, will look for the exact code snippets later, but in summary from what i read earlier when i first came across these claims last month or so, any activity that happens with a comment is also federated: Creation, editing and deletion, so barring any cache that will eventually expire, or an instance going down, the lifetime of a message will be replicated across anything that federates with it.

And yes, a patched instance could just ignore deletion and save everything, but at that point you’re fighting a rogue element and the rules change, we’re discussing the normal, designed behavior of the software.