It's unlikely and almost inconceivable to get to $5, though, because the main benefit of having a large, distributed network is that it takes a sizable amount of people to sell out to drop the value. This is inertia of a stock. You can better believe for the number of people panicking and selling off there will be an equal or greater number of people holding on to it, and that's why I can only see it dropping 50%, maybe 75% at max, in true market free-fall conditions.
I believe drop to $5.00 could only happen if anti-bitcoins laws are approved because of fear of laundering money. Bitcoin would still be used but there would be almost no demand and extensive supply thats why such low USD/BTC
Even that wouldn't happen in most universes. Knowing how resilient us Americans are about making our money, you'd watch the American BTC culture suddenly endorse the Euro. Suddenly every teenager who's ever mined would be reading the WSJ Forex sections.