Hmmm... it would currently take a market sell order of 2.3 million Bitcoin to drive the price below $1,000 on Gox. Since selling "at market" millions of dollars of anything is moronic, I doubt even the "million bitcoin" individual/group converting into fiat would cause that amount of chaos...

Edit: @aylwood My mistake. I meant 2.3 million in Bitcoin which was accurate at the time posted.