Being able to "attack" a system because you have a password/private key and really attacking it, are 2 complete separate things. If you are too stupid to understand that, than I can not help you.
Your scenarios are based on "I have infiltrated everything. I have even magically infiltrated you air-gap machines". If you could really do that, why bother with bitcoins? Just get access to all nuclear silos and threaten to bomb everyone.
So are you saying that it is impossible to combine 2 or more attack strategies in a giant onslaught?
You do raise a valid premise: Will a global currency system have any practical use in a post apocalyptic global scenario? Eg. global economic collapse, global police state, global nuclear winter, world wide killer virus outbreak, giant asteroid impact, sentient computers, etc...?
Perhaps not. But if it would, then the question is simple: What can we do now, to maximize its utility both today and at such a point in the future?