Bitcoin mining could use any amount of electricity given that the block difficulty adjusts to the prevailing hashrate.

If more people pile in to mining then the difficulty increases and total $$$ spent on electricity will increase. Conversely if mining hashrate declines then difficulty is decreased to compensate.

I'm not sure how the difficulty adjustment would cope with a severe and abrupt change in mining hashrate (take it to the extreme and imagine the hashrate drops to 1/1000th of what it is now, there are going to be a lot of unconfirmed transactions out there).