If all miners could change chain instantly, and if all miners would always optimize for the best short-term profitability, then Bitcoin Cash would soon be a winner and Bitcoin would be dead. Without miners on the Bitcoin chain, we'll never get to the next difficulty readjustment checkpoint, and it will forever be "too difficult" to mine bitcoin. This is the selling point of Bitcoin Cash.

The Bitcoin Cash fanatics strongly hope that this will take place. Personally I believe most mining pools will stick to Bitcoin, there are too much stake at hand - if Bitcoin ("SegWitCoin") was to die, it would take years before Bitcoin Cash gets into the same position as Bitcoin is today. We'll probably see a certain percentage of the mining power flip-flopping between the chains every time one of them gets more profitable than the other, though.

Seeing the mining difficulty chart at https://bitcoinwisdom.com/bitcoin/difficulty there seems to be an insignificant amount of defections from Bitcoin mining, so this far my prediction has been right. Of course, there is quite some inertia, we'll see what happens Monday - but I predict the Bitcoin Cash value will fall unless a significant amount of miners are changing horse on Monday.