@ 100 USD per BTC = Difficulty 240,000,000
Net profit over 1 year: -0.58 USD
@ 150 USD per BTC = Difficulty 368,000,000
Net profit over 1 year : -5.46 USD
Maybe at that point people will keep their mining rigs turned on in the hopes that eventually BTC will appreciate in value past $150. I don't think people who get mining gear from ASIC/BFL will turn off their hardware unless they are loosing a lot of money. You just don't chuck your $2,499 machine into the closet on a loss of 50 cents. People will foolishly keep hoping while it continues to get worse.