If Mining BTC Even with free electricity cannot pay the mining equipment in a year, that will be the doomsday of BTC, 2000$-2500$ is the limit.
Do you think btc price keep same for 1 year at the bottom ? Some miners know when they mining profit is low, they just don't sell their coin yet.
And you know, when the price of btc keep falling, many miners will stop mining, but not all of the miners. The survived miners will keep mining because they know the difficult of bitcoin will drastically falling due many miners stop, and they can earn more btc from mining.