Good point about the Scots Guard. Wonder what would happen to that unit if there's a split.
Might (have) become part of an independent Scottish army, might stay as part of the British Army. There's still a few thousand Nepalese serving in the Gurkhas and they come from half way around the world, not just over the border. Don't see why the unit couldn't continue to exist.
Another example is the Swiss Guard that serves the Vatican - and would make a great addition to the playmoworld.