They would miss having the right to perform weddings, I imagine...?
St. George of England I doubt it. This is how it used to be in the UK years ago. The wedding was conducted at the KH and then the couple went to the Registrar's Office for the legal part, or as often happened at our KH, the Registrar came along to the KH, sat through the service and then did the signing of the register.
Yes it's always been that way in the UK. I think now the registrar observes the ceremony and then ensures the couple & witnesses sign the wedding registry.
I presume in Norway officially registered religions are permitted to perform their own legal ceremony. Once Watchtower is longer registered it will be as in the UK, the registrar will attend the kingdom Hall in order to officiate the legal part of the ceremony.