Archive a forum / read-only version - or - create a copy and continue to provide the forum?

If they’re in the EU (EDIT: Or might possibly have users from the EU, or, maybe have users that might move to the EU, or have users that might claim that they live in the EU) they should certainly listen to you. Whether it’s easier to run and maintain discourse indefinitely or run a static site and find out how to do a sed command to do a recursive replacement is up for grabs, I would say.