Hobby miners with small farms can mine essentially forever at a small loss. Big miners will not be able to mine for long at a cost due to space and electricity cost (assuming they already paid for their hardware and it wasn't on credit). If big miners fail they could sell off all of their reserve coins, tank the price of BTC and in the end all we would have left are the small hobby miners again.
Well big miners will be lossing on a lot of gains if they dont risk for a while. Nobody said it would be easy. Also if they stop, these smaller miners will get a bigger slice of the pie.
It's a game of chicken. The miners can't stop mining because if they do the amount miners can make will go up, so they may as well continue mining and hope the price goes up. Think of it as dollar cost averaging on autopilot.
The biggest impact will be that they can't continue to invest in new hardware. As the demand for miners goes down the companies selling them will shift to just mining with the hardware that they make. Eventually those companies will not only reach 50% of the network, but in fact dwarf all mining pools combined. It is my prediction that this will occur as soon as 2015.
When this happens the future of Bitcoin will be cast in doubt, there will be panic and drama, and hopefully a solution will be found.
