War would see an increase in bitcoins price but a natural disaster? I'm not sure. It depends how many places it affects since if it's just a small country or a few islands it wouldn't affect the price at all even if the people there had to spend all of their bitcoins.
It has a point. People today did not really give attention to bitcoin, some people ises but not all therefore we can conclude that it would not be affected because of the high population a specific location a disaster will come. With this we can say that the market as a whole will not be affected.
The title of this thread says "global disaster" not local or only on a specified country , therfor there is a posibility that the market will decrease because people will expected to sell so that they can have a money to buy foods and other important things in life .
There is also a chance that cryptos can became stable if ever there will be no electricity available due to disaster because people cannot possible cash out .