...About ETH miners (GPU miners). They will move to mine other coins but 99% will have to quit. ETH is $200B network. ETC is $4B. So if 2% of ETH miners will move to ETC mining difficulty will double making it unprofitable to mine. And price will not fallow. Its the opposite. Difficulty chase price not price pump because of difficulty increase.
Owners of GPU miners will still have to make a choice and connect their machines to another network. And wherever they connect their miners, there will definitely increase the complexity. The problem with increasing network complexity is temporary. When mining is not profitable, it entails disabling miners and the next time the complexity is recalculated, it will decrease, which will make mining profitable again.