If you include the hash rate for the ETC, the difficulty is 20% higher. So If the ETC is not mined as much, the difficulty of the ETH will be much higher.
If ETC keep dropping, ppl will move their rigs back to etherum and 20% higher diff. But If this happens I expect the Etherum price to climb around 20% as well.
The Ethereum total hashing is about 20% higher than a month ago. I think if the trend continue, it will not be profitable for many people in winter.