But let us think for a second how will bitcoin be useful to us should WW3 actually happen?
This question should be extended to people in various condition (such as live far from WW3 or live in country directly participate in WW).
The most important thing is if you live in a country directly affected by the war, surely people would migrate and seek shelter. Bitcoins can be helpful for doing this as you will not be carrying your country's local currency. I am sure now that people would be buying crypto in fear of the war happening.
For people on such unfortunate condition, they probably should consider brainwallet if having electronic device or paper (contain recovery words) have serious risk of being stolen or put you at additional risk.
Brainwallets are not recommended to be used in general because of fallible human memory. But in special situations they could be very useful, for example when fleeing a country as a refugee with only the clothes on your back.