This is a what if topic, and again nothing goes down in an instant, even before two countries start war it will begin from somewhere, now let's say everything seize to exists with crypto, isn't this only possible if Internet stop working around tbe world? Because it's impossible that all coins just decide to die including Bitcoin.
As you said it is only a what if, and as the he said the scenario was instant. As for wars, I think this is possible if there is a nuclear or equivalent involved but it is not just the crypto that will get wipe there but possibly the whole universe. If there is no internet, people can only stop transacting but cryptos are still there functioning. I think the ones that can kill them digitally is if there is some kind of a virus that will break their codes. I think the quantum computing that they are saying is also possible as one of the lead.
If such thing is going to happen it will happen very slow, the red flags will be there and there will be enough time to exit the market, but let me stay on topic, that if crypto just vanish tomorrow, what will happen.
I will be stucked, because everything about me is crypto based, apart from few stocks that I invested in, I am more into Bitcoin and trading than anything else, I will go broke if this happen and will have to find other ways, it's not the end of the world.
Maybe you will rather feel shocked but this scenario is the reason why it is important to diversify on different types, so that when something bad happens with the other, we still have a chance left.