My electricity price comes to around $0.11/kWh. Even if few weak hands sell off their rigs, the new comers will still use those rigs to mine. I don't see the # of GPUs mining to reduce in number - but rather they are increasing drastically. Look at the hashrate chart from Jan this year to now.

I don't see the difficulty going down either. But, I'm sure when the electricity charge equals or goes beyond the value of coins rewarded, few miners may stop mining. But even then, most of the heavy hitters are not bothered about the current price levels and are accumulating the coins. That is becoming a problem for small scale miners unfortunately.

I really hope ETH stays POW and they implement something similar to Charlie Lee's vision where miners set their own price for taking up transactions, and pick up only the transactions which fulfills the price criteria.