the characteristics of bitcoin is what gives it value, not what it cost was to mine it. Of course, there is less incentive to mine it if the market value goes under production value. But the sole fact that there is demand at all, means it is useful to enough people to give it that value.
exactly. the only reason why people started looking at irrelevant things to speculate the value is that they couldn't predict the bitcoin price so they needed things like hashrate that could be measured.
but what they forget is that miners are workers that are getting paid. if the economy is good their check is fatter so more workers are sign up for employment and if the economy is bad their check shrinks so some of them quit their job.
in the end the economy is there. bitcoin continues providing its utilities whether the employees are getting paid a lot or a little.