How would bitcoins "crash"? The value of bitcoins has been fluctuating like crazy over the last week, experiencing exponential growth in the BTC to USD valuation. There is no way that that can be maintained longterm. What would make it crash?
If there are no more buyers at price X, then a seller has to lower his price by Y. If there are still no buyers, she will have to lower it more. If there a lot more sellers than there are buyers the price can drop very quickly, just as right now there are a lot more buyers than there are sellers and the price is rising very quickly.