I think that scenario is a long way off. It's not that we will need nuclear codes to defend against a Russian attack, it's that our continent will be destabilised by a Russian push westwards to retake its former empire. And it's not even certain that the Russians could succeed, it's the mere fact that they might try.
This looks very much like 1936 with a belligerent expansionist country being appeased and an isolationist US. Only this time it's much worse because the people leading the US are fascists trying to destabilise European countries
...and the weirdest and stupidest people in the world are Trump supporters in the UK. Not-so-crypto fascist, Nigel Farage, must be creaming his pants.