Retiring a TLD is cruel to anyone using the domain, especially with the prevalence of TLS. Just as retiring "land" that someone paid for and is living on would be cruel.

The tendency for technologies to evaporate and be migrated to replacement for $reasons is too frequent.

Domain TLDs should remain constant. If .gb no longer represents a geopolitical entity then transition it to a new manager with a contract that stipulates maintenance of established domains. Don't set precedent for pulling TLDs out from under people.