They can never buy all the coins, or even all the Miner. The most hodlers will not sell all their coins, i think. The price would be too high to sell all of them and a big part of coins is lost, so they will never buy them. And all the Miners around the world, oh no, that is impossible too. All over the world there are different ways to buy a miner or run it online. Many of them will not sell everything if the price is very good, they will always keep a small part and protect it.