Everyone will get their old miners back out and turn them on again ;-)
This cant happen, even if the price is 10 k per bitcoin, old miners like gpus or usb will not make roi in years.
ROI has nothing to do with it.. once a miner is purchased, that is a sunk cost. Once you have it, the only thing that matters is operating costs (electricity, mostly) .. So long as bitcoins returned are greater than current operating cost, the miners will be turned on. It makes no difference that it will never make ROI. At this point, it is about reducing losses, not making a profit.
Sigg