I see cryptocurrencies as another opportunity to diversify, although as you point out @arnoldz61, Crypto is a hedge bet that the apocalypse will not be equally distributed. If it isn't, there could be vestiges of the old backbone still blinking like a hyper chipmunk on crack (blinking, as in ones & zeroes). Some other possibilities for post-crash cryptocurrency connectivity are mesh networks, radio networks and a few other hardware heavy point to point options, like microwave, if I'm not mistaken.
Admittedly, I'm not familiar with the network requirements of the blockchain, but if there is anything running and spread wide enough to support activity - that cryptocurrency could come in handy. Imagine ordering supplies from a neighboring country that is functioning at a much higher level, for instance. or even contracting a retrieval op from said functioning Iceland, I mean, country.
I don't think a radio signalling network could handle the data flow needed for a block chain to work. And why bother with any currency, unless you have more than 100K in your account. We don't need wealth, we need food and shelter, so let's take care of that. We need to be independent.