Sub $200 will take a lot of miners out. Can the big farms even sustain below $150?
It would put them out, but not indefinetly, because the difficulty would eventually lower back down due to fewer number of hashing power, and
it would once again be profitable to mine.
I believe the big mining operations owners are quite interested in bitcoin, so the profitablility in negative would just make them store coins for future use , and
the mining should continue. However i dont see bitcoin going below 150 ever again, reasons for that to happen would have to be catastrophic failiure, and that is not likely to happen.
cheers