Somewhat useless in the place where you are where networks are down(but so does your digital payment platforms), but obviously very useful in a way that if you can immediately leave that place and go to a country that's at least not(or not yet) affected by the war.
If you're still planning on somewhat staying in the war-inflicted country, then obviously you don't convert 100%. You still need cash for resources.
Probelm is you won't be able to take cash out after a while. It's horrific, the ATM machines stops giving out money since the government is desperately trying to control their economic situation and at the end there is a limit on how much you can take out as well therefore I don't think that this is something that would work.
When you have bitcoins, you can convert it and encash in any card in any country at any moment therefore for me that was the only thing that kept me going and I was able to escape as well.
Also you can very easily use local bitcoins and encash bitcoins directly in the card that you intend to pay in therefore this is very helpful as well since local and international cards do charge a lot more than you think ! More or so it's around 10-12 pounds in total for sending 60$ and with bitcoins you can get it done in 2-4$ !