Your instance will still exist, and federation should continue as normal if you manage to reclaim the original domain.
If you have to switch to a new one, however, federation will be very awkward. Other instances will essentially treat you as a brand-new instance, and mirrors of old content will be “orphaned” and no longer sync.
What the person using those links does not realize is that a Creative Commons license relaxes restrictions rather than imposing additional ones.
Everything you create is already protected by copyright by default. If you publish an essay and don’t append any license to it, nobody may republish or remix that essay without your permission, unless an exception like fair use applies. The exact restrictions will depend on local laws.
By using a Creative Commons license, you choose to forgo some of those copyright protections. Thus the comments of the person you replied to are actually less protected than yours or mine.