There's more to it than multiplying the current price by the number of coins in existence: you need to consider the questions of liquidity and what an attempt to sell a non-trivial amount would do to those exchange rates as people start questioning whether they want to put more hard currency in. Cryptocurrencies are the weakest form of fiat currency and that means that there's a very real chance you simply cannot find enough buyers at the price you want to pay.
This can technically happen with other currencies, of course, but they're so much larger and more stable that it's orders of magnitude less likely. You need a world-shaking catastrophe not to find someone willing to take USD because so many contracts are written in USD, and there's plenty of need to pay taxes or interact with government contracts and employees.
This can technically happen with other currencies, of course, but they're so much larger and more stable that it's orders of magnitude less likely. You need a world-shaking catastrophe not to find someone willing to take USD because so many contracts are written in USD, and there's plenty of need to pay taxes or interact with government contracts and employees.