It is a very good question and you might say the same about having your savings stored in banks that might be vulnerable to hacking or be located in a sensitive area. In these wartime situations it could become very difficult to access these wallets or transfer them, not to mention the possibility of your hardware storage getting damaged through all sorts of ways. It seems much more useful to have a (stable) cash currency available to hand or even precious metals like gold / silver if you think you're going to need to barter. Bitcoin definitely isn't worthless but it'll definitely be safer the further away from the war zone you are, if you're in the midst of it then storing it online might be safer.