The  scenario described seems quite realistic,  the same  risk was described in a zerohedge headline today.
 With bitcoins huge coverage lately  I'm surprised it has not been more demonized in the MSM,  I would have thought that would be the first defensive reaction of those who would like to see bitcoin fail.
The possible defenses that I can think of are
a)  back bitcoin with reserves ( of gold probably), like a central bank, just enough to put some sort of floor on how far the price   could  fall in the case of a crash.  I can't see this happening,  who would pay for it?
b)  more exchanges,  somehow supporting more graceful price drops when demand is low.
c)  access to more btc  denominated  assets,  allowing current btc holders to cash out without going through exchanges.

The key is to  get money flowing within the bitcoin economy, and providing a wide range of exits to try and avoid panic selling when the price does fall.