"If Bitcoin prices drop below the cost of mining" miners just stop their operation and use the money they use for electricity to buy Bitcoin. Free market will be adjust according to the supply and demend. Nothing to be worry about to much.
That will be a huge mistake, I have seen people say that the bitcoin they mined back in the day when it was not profitable to do so was in fact the most profitable of all, the miners have a lot of money they are not going to suspend their operations just because it is not profitable at this time, since they know the price of bitcoin will recover and the bitcoin they get can be sold for a profit in the future.
Suppose your cost of mining is $6000 per bitcoin and the price of a bitcoins drops to $5000. Are you going to mine 1 BTC for $6000 or are you going to buy 1.2 BTC for $6000? A smart person would stop mining and buy the 1.2 BTC.