Well not sure to be honest. They have converted a lot of their btc into bch and supposedly  now hold over 1 million BCH.

Yet BCH has plenty of other risks associated with it and is unlikely to survive if BTC falls to much.

yet Bitmain also have their IPO coming up and would need a relatively high price for BTC and BCH in order to sell their IPO successfully, so perhaps they will defend the price to some extent.

however take note that bitmain has performed very poorly in Q2 and Q3 this year. They have burned through a lot of their cash while their last few miners are terribly inefficient and have by and large failed, with one of them being less efficient then a GTX 1080 TI, so not sure how much exactly they have left in the tank to defend the price.