With US bombing Iran, talks of WW3 seems closer and closer. I am, of course, not wishing for this to happen as nothing good will come out of it. But let us think for a second how will bitcoin be useful to us should WW3 actually happen? First of all, expect chaos. Fiat Currencies would most likely decline. Governments would need to print more money to budget for fighting other countries. This will surely lead to inflation. This is where crypto would come in handy. Bitcoin can be a safe haven for most.
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.
If WW3 happens, you can forget about Bitcoin. That's because there will be a nuclear war that will ensue chaos worldwide. The least thing people will think about is Bitcoin. They will look for things that will guarantee their survival (mainly food, water, and shelter). My guess is that BTC's network infrastructure will be severely damaged, as several nodes and miners will go offline. It will still be alive, but its operations will be disrupted.
Let's not forget that Internet access will be limited during a major global catastrophe. The only way BTC can survive is if nodes and miners live in space. Internet access via satellite would be a must for people to be able to perform transactions on the Blockchain without disruptions. We can never tell what will happen in the future, so I'd hope for the best.