Difficult to know what is going to happen.

On the one hand, it seems very difficult for the US and especially the European Union (because they are neighbouring countries) to see Russia invading and annexing completely Ukraine in the way they did for Crimea.
But on the other hand, Russia (and Poutine) consider that Ukraine is their back garden (and they have a very long history together) and therefore cannot accept to see Ukraine joining NATO and western democracies.

Is the current massing of Russian troupes along the border the start of an invasion or only a demonstration of power acting as a warning, it is impossible to guess.

However, it is unlikely that expats would be targeted as it would immediately increase the reaction of occidental countries. British expats are very unlikely to be different from other expats.