Life is rather uncertain nowadays as anything can happen at any time and we would be caught off guard. Thats also one way to describe the current economy at this stage. With the worlds economy expanding and expanding there have been more crashes as the years go by and they are becoming more frequent and some say at any moment one could happen.
So you are left with a situation in which the money you currently own, fiat money: the dollar bills & coins, will become worthless and you cannot even buy anything you need to survive on a day to day basis. In this situation, people will have to resort to a system of bartering like in the stone ages. I guess if you have a lot of stuff with value you can trade that would be great, but a majority of people dont have such a stash. Things can get ugly real fast.
Therefore, in such a doomsday situation you have to come up with a situation in which you can trade with people in order to survive. There are two solutions I can come up with, either using precious metals such as Gold & Silver or using Cryptocurrency. Considering that fiat currency is useless, Cryptocurrency might raise in value so that it can be useful as a means of trade as long as the Internet still exists which will most likely be the case.
For paper money of world states to suddenly become completely useless, a global catastrophe must happen. If the paper money of the state becomes useless, not so much hyperinflation occurs, the state itself should practically collapse and cease to exist. I think that at the same time the Internet will disappear, and with it the cryptocurrency. Therefore, cryptocurrency can only exist in a high-tech society. If a global catastrophe happens, the satellites will fall and the Internet will disappear. If the Internet and cryptocurrency exist, then the national money of states will certainly exist. Therefore, I do not think that cryptocurrency will ever save us from a return to barter relations.