The cost of one Bitcoin mined finally catches up with the price, and reaches $700 on average. This means that miners have to sell around $2 million of BTC each day, because they have to pay their electric bills in currencies other than BTC. This means we need $2 million of daily fresh cash to keep the price at the same level, around $1000.
why do you think it will catch up? you don't know what the price of bitcoin will be at that time.
It will catch up, because, hey, free money.
This is a very basic economic argument. New miners will join until it is profitable to do so.
As for not knowing the future price, you got a point there. But, if the price stays the same, which was the OP all about, then, 3 to 7 months. If price falls, perhaps sooner. If price falls even more, perhaps no catching up will be needed. If price keeps rising, difficulty will try to catch up, and it could take longer.
But, my argument is all that this electricity cost will put breaks on Bitcoin price, and even if the price rises, the breaks on the price will be stronger and stronger as difficulty rises.