Dude, you talking about NUCLEAR war! That would be the time when you and me will have to find the shelter underground somewhere on the horizon to save our own asses man! Who would think about bitcoin and even dollar bill when people will be killing each other for food, water which is not radioactive.
Our own lives will be more important than the bitcoin or blockchain. There will be nothing available in the nuclear war. The only thing that will keep us going on is survival instinct. Thats all.
It will be hard to survive in a nuclear war, it will affect the world not just 1 country once it is release and I doubt if that happen people will mind their investment. We will mind ofcourse ourselves and our family safety. The war alone is already hearth breaking and affects many countries economy and safety. What more if Nuclear been used, hopefully it will never happen and peace will be find as much as possible.
If a nuclear war really comes, what we should consider is whether we can still live? Will there still be a country at that time? Whether there will be human beings is a question, but I think at least there will be no nuclear war in the few decades we are alive Because although there is a war at present, it has not reached a very large-scale war, and human beings have not formally contacted alien civilizations, and cannot immigrate to other planets, so what is the benefit of launching a nuclear war now?