If BTC price falls 50%, and hashing difficulty stays the same, will transaction fees rise by 100%?

If BTC price falls 50%, and hashing difficulty stays the same, will transaction fees rise by 50%?
Or will it be up to the miners to reduce fees and absorb part of the decline in profitability?
Moore's law predicts that computational power can not maintain the pace of Bitcoin hashing rise in difficulty, and Moore's law's pace itself is unsustainable.
What will happen when Bitcoin mining becomes uneconomical due to energetic considerations?