The hashrate is increase exponentially and certainly unsustainable. What will happen if one day, the hashrate is so high, no miners would profit from mining it?
difficulty adjustments
Do you think the bitcoin hashrate will decrease at some point? Historically, it's been increasing all the time? When do you think it will happen?
That's not completely true... The hashrate has had drops in the past... In this case the diff was adjusted downwards.
To answer your question: for most miners, if they cannot make a profit, they'll shut down their gear... Hashrate drops, diff drops at the next adjustment, the leftover miners can mine at a lower diff (making more profit)...