Wales is part of the Kingdom of England, under the "Laws in Wales Acts 1535 and 1542" [3].
Without Scotland, it becomes the United Kingdom of England and Northern Ireland, leaving the Kingdom of Scotland. Scotland would be assigned an ISO 3166 code. SC, SO, ST, SL, SA, SN and SD are all taken. Perhaps they can have "AB" for "Alba". The "GB" code would be unassigned.
Without Ireland, it becomes the United Kingdom of Great Britain. Northern Ireland presumably joins the Republic of Ireland in this case.
Without both, it becomes the Kingdom of England, the Kingdom of Scotland, etc. England would then need an ISO code, "EN" is available.
[1] https://en.wikipedia.org/wiki/Acts_of_Union_1707
[2] https://en.wikipedia.org/wiki/Acts_of_Union_1800
[2] https://en.wikipedia.org/wiki/Laws_in_Wales_Acts_1535_and_15...
[0] https://en.wikipedia.org/wiki/Countries_of_the_United_Kingdo... and https://en.wikipedia.org/wiki/United_Kingdom
[1] https://webarchive.nationalarchives.gov.uk/20080909013512/ht...
I assume no, so perhaps it's ok for a Kingdom of Great Britain not to include all of it :)
FWIW, Serbia almost kept with the Yugoslavia for as long as it had someone to unite with. It did turn into Serbia and Montenegro in 2003, before ultimately splitting in 2006.
It even got a first case of ISO country code reuse with CS (hi Czechoslovakia), but I don't think there was ever a TLD .cs for it.
Meh, it will become "the United Kingdom of England and Overseas Territories" or something to that effect. UK is a brand and a symbol that Westminster will never abandon. Serbia, for example, tried really hard to remain "Yugoslavia", and if it weren't for the tensions it generates, that name would still be around.
"The medieval conquest and subsequent annexation of Wales by the Kingdom of England, followed by the union between England and Scotland in 1707 to form the Kingdom of Great Britain, and the union in 1801 of Great Britain with the Kingdom of Ireland created the United Kingdom of Great Britain and Ireland."
If Northern Ireland leaves, I guess the UK no longer exists, and we switch to ".gb". Could clone .uk at .gb for a while (ten years?) and give people time to switch, but seems more likely Nominet would prefer to just charge people twice for a .uk and a .gb.
If Scotland and Northern Ireland leaves, that leaves us as just "Britain". Maybe we create a new ".brit" (or whever the 2 char country code will be), and give time for .uk to disappear again.
Wales wont leave.
[edit] I just saw emmelaich's comment that .gb already exists.