Let's do the math and do not mix hashnest case with real efficiency. If bitmain or whoever has access to cheap electricity, say 3 cents/kWh, they can have 150 days ROI even at 1.7 exahash (about 250mil diff). At 1 cent/kWh the breakeven hashrate is at 2 exahashes.

So the hashnest will have to go down (at charged 0.09 USD/kWh) but it in doesn't mean miners should be physically shut down.

edit: I am talking about S7