It's not a magnett link, but just the same, I linked to a torrent file. It is not a Copyright Infringement.
But if the link is a link to a content that violates the Copyright Law, then there is potential issue.
Linking by itself is vague. There are countries that don't consider links as Copyright infringement, because again, these are just links. Only the host is causing piracy / infringement. However, there are countries that considers linking as an act of distribution of an infringement material, so it is illegal for these countries.
So there’s no way to scrape an instance to back it up as a third party?
If you have a script, then you can. You can submit links to web archive services and they'll scrape the site to archive a copy of it.
I understand someone not wanting to have pirated content on their instance, but do you think mods will go out of their way to un-federate?
Oh yes, definitely. You can count on instances defederating/blocking instances tolerating Copyright infringement activities. There are various blocklists available for instances to use, and there are groups where admins share and discuss these things.
So, sooner or later, an instance tolerating Copyright infringement will find itself isolated and potentially an island.
It can remain online as a regular site. It just won't be federated with anyone.
One more thing. There are blocklists and admins who will defederate instances just because they are not blocking certain instances. Thus, if I am running my own instance, I might be forced to defederate from an offending instance to avoid being defederated by everyone else.