I think it’s ok to require the original instance to be online, an insecure migration should just be telling people to follow a different path imo. I think giving communities a low friction way to be nomadic would ease concerns about deciding between self hosting and using existing instances. Users could perhaps be presented with a popover to communicate the change and maybe have an archived link to the old community path. It would also be cool if you could initiate a migration using just backed up config secrets in a new instance.