Very interesting and informative and critial. I don't think there could be a solution because the emphasis on digital cash requires a digital reality. As luzcypher pointed out even fiat is exposed to this risk.
An interesting point, My family are Roma and one of the things I always found interesting was that most of the women in my family collect fine china, Crown Derby to be precise. These plates and pots are hand painted and often painted with gold. I once asked my mam why she collects so much of it. She told me the story of the old days when travellers (roma people) had no access to banks and on hard times the plates could be sold because they don't lose value. It's not a viable thing to carry around in your pocket but it comes back to the old Gold. When the power goes down the best thing you have to trade will be gold or valuable metal. The same thing that mobile phone your carrying has in it. If in tiny amounts. 
I don't think that is going to change. If you don't have gold, you better be damn sure your useful somehow or those War lords are gonna put you to use anyway they like.