I am not so sure that a lower price or price descent would cause BTC to go away or be endangered.
I think the price of the BTC will be directly related to the hash power. If BTC goes to, say, $1, then the hash power would be reduced to 1/250 of the power in order to produce the same $/hash. A hash takes x joules (watt-seconds) to do, so in terms of electric power a hash takes a fixed cost to compute (the cost goes down with ASICs etc). So if you spend x joules to get 12.5 BTC in a block, you have to take into account how often you will be successful, which is based on the number of other miners on that chain. The more miners, the more rarely you win. So the hash power will not disappear if BTC price goes down, but will decrease such that the mining cost is balanced with the block reward. There is a negative feedback keeping the market in a balanced state.
Perhaps this will play out in the unlimited results.