FB's move strikes me as similar to Germany's pre-WWII invasions. Will take incredible popular, political will across the world to stand up to and won't come cheap to the countries that do it. But the cost of not doing it should be obvious in this framework.
The whole issue is more akin to a treaty negotiation than a criminal law enforcement. The Austrian law side of things is just one of the tools available to exert power on FB. FB has their own levers to pull like they demonstrated in Australia.
To think that this issue will be decided anything like a normal criminal case that just comes down to an interpretation of law and fact will cause extreme cognitive dissonance.