Between Sept and Nov 2011, mining difficulty decreased about twofold in the wake of ~75% plunge in BTC price (from ~8 to $2).
Right now, we already have network hashing speed down to 229Ph from 330Ph (~30% decrease) following $320 to $230 plunge (a fast ~28% decrease in price).
In conclusion, network hash will probably decrease to ~150-160Ph if and when BTC drops to $160-170. perhaps, this would be a bottom just as it was in 2011.
The lowest BTC can go within so far observed bear markets is ~$72-84 ( similar percentage to 2011), not that would be very desirable.
I am have trouble seeing network speed at 229Ph
I find some est. at 289ph and at 273ph
As to how low can the coin drop?
I wonder if it could go under 100.
I did purchase some at 237 usd today.