It will happen when some rich person decides to buy all of your bitcoins and mine the rest them sell them back at extremely inflated prices because the demand will be high and supply will be at a near zero. Imagine that. Bitcoin is only around 450 dollars at the moment. Someone rich enough could buy all of the bitcoins for a little under 10 billion (assuming all 21,000,000 bitcoins are mined). At that point, he can manipulate the hell out of the market. If he were to sell possibly a million of the coins before the price starts going down due to saturation, he'd make back all the money he spent on all the bitcoins. He could sell maybe another 10 million for maybe 2000-5000 a pop.
All in all, in my opinion, this will be the only way the price would ever reach that high. It is like you owning a small piece in the company through stocks. The market is full of manipulations due to media coverage and lies many of the times. Those are associated as pump and dumps which is exactly what would happen with a person owning so much bitcoin. They hype you up, get you to invest in it, and then they dump, liquidate, and file for bankruptcy and run with the money. Simple as that.