No one can predict what exactly will happen in the future. In the event of a nuclear war, they can turn off electricity and the Internet, no currency will have value.
I wouldn't say no currency would have value in this situation, but at one point their will be something that rises above all the be worth something, the gold companies will say its gold, silver companies will say its silver, and so on and so forth.
But yes, at some point all fiat-currencies are going to have to crash and we just have to wait for this to occur. I think that by the time this happens we're not going to even be able to use Bitcoin as we've entered a time where the internet and infrastructure has been destroyed (this is if fiat dies too)
Good point.
Such a situation would be extreme and call for extreme measures. Value probably in such a situation would return to the basics, food, shelter etc...
Exciting to see tough witch currency will hold the most value the longest, IMO fiat money is pretty weak in that regard if you compare to other resources that currently hold value the same way fiat does.