Why does is matter, you say,

if a currency disappears, completely tanks?
Because thanks to the internet, and 'just in time', (hold that product until you need it, then poof! it appears -just in time-), and credit, we are so connected that when you eat a hamburger the meat was grown in Chile, the lettuce came from Mexico, and the onions grew in the Imperial Valley in California. So you say, don't eat the burger, don't go to the doctor, who needs them anyway you say? There won't be an herbalist either, and forget exotic foods like veggie nut patties.
Something will go away, someone won't be able to buy a book, pay a bill, take a child to the doctor. So the lights get turned off, the child stays ill, or gets worse, nobody reads.
It's been an amazing run. We have gotten to live at the peak point of a high culture, much better than a cold dank cave. I still keep hoping it's going to some how pull out.
Julie