If they shutdown all the mining farms, the network will have slow transactions for a while, depending where it is at the regular 2016 block difficulty adjusts, which usually takes about two weeks. When the diff adjusts, everything is back to normal, so no Bitcoin doesn't really mind, its been designed around that.
Shutting down exchanges and farms, of course affects the people involved, they are losing their source of income. But on a global scale, it matters little. Again Bitcoin doesn't care if there are a 100 miners or a 100 million miners, and certainly doesn't care if exchanges exist at all. This is an out of Bitcoin thing that is convenient for non miner people wanting to acquire bitcoin with the only kind of money they have: fiat. If they somehow got altcoins, they can dex p2p exchange those for bitcoin, without the need for centralized exchanges anywhere.
To answer OP question: What happens? Not much really. Just a temporary slowdown of transactions, that's it. It has happened before...