That presumes bitcoin is the only crypto currency, it isn't, and they don't all rely on mining like this. Secondly, as miners drop out because they can't profi

That presumes bitcoin is the only crypto currency, it isn't, and they don't all rely on mining like this. Secondly, as miners drop out because they can't profit, those who stay in see profitability return. It's self adjusting, there will always be profitable mining for those with the best mining rigs.