Hi ! First message here.
If a global disaster would happen on earth ( And I somehow don't wish it ) Would the value increase or decrease ?
I'm not talking about solar flares or EMP. But more like big wars or great natural disaster.
What are your opinions on the subject ?

It depends on the location where it would happen, if it would happen in regions which are considered wealthy, then definitely yes. The price of Bitcoin would increase because the wealthy regions of the word are strongly connected and their currencies also.