Why not sell the coins? The market is big enough. I can't see why someone would mine coins without selling them as they are mined, otherwise you don't realize your profits. When there is enough cheap dollar in the market, there would be someone else who believes the coin price would rise at a later point and buy BTC for profit.
If miners sell, it means more money has to enter the system in order to keep the price from falling. And conversely, in the absence of more money entering the system, miners can't sell their bitcoins without crashing the price.
The thing is you have to sell it sooner or later or you won't make a profit. If you sell it to such a price that it's significantly lower than people expect it to be, someone will buy it so they can be sold at a higher price later. It's extremely easy to open both short and long positions on BTC market, so the current price should remain close to its expected price.
