Good answer, although you don't answer his exact question.
If everyone sold ALL their bitcoins right this instant...
The answer is this is likely impossible. It would start the catastrophic crash (ie. only the first 1% of bitcoins would likely get the $250/coin we see now then it would go down quickly) we all predict will happen sometime in the future. If someone sweeps in last minute to buy the rest of them, it will make the bitcoin useless if one person holds them all and the demand is gone.