As of now, the profit margin of GPU margin is far too high for people too stop mining. So once you've made the initial investment to set up the rig, it would take a very steep drop in price to make people stop mining. So it does not directly affect the price.
That's a very good point. If you already have the hardware, the profit calculation is totally different than for someone just starting out. Another reason there's a big lag between the amount of mining going on vs the price and difficulty.l