This reminds me of the Chinese revolution, where after the Communists took control of everything except Taiwan, many international organizations continued to insist that Taiwan was the actual representative of China, and Taiwan held the Chinese vote at the UN until 1971. So that's about 22 years of pretending.
I'm no fan of either communism or the chinese revolution, but I always thought that was ridiculous, that a country so big as China had no UN representation except via Taiwan, and that Taiwan held a permanent member UN security council seat.
If, for example, Russia conquers all of Ukraine, then how long will some guy sitting in London keep pretending to be the Government of Ukraine? At some point, all the social media accounts, internet registries, country codes, etc -- they have to be updated to reflect reality.