So, I wonder if Lemmy instances would be responsible for the instances that federate with them. It's my understanding that the Lemmy instance doesn't send the user's data to other instances, rather it is just posted, and the other instances copy it onto their local instance.
It's almost like those reddit services that would show deleted content. A user can delete their profile on Reddit, but Reddit isn't required (that I know of) to go to these services and make sure the user's data is being wiped out.