In my opinion, if calculator again the price of Bitcoin today is $2400 and the price of Bitcoin Cash is $400, we will have $2400 + $400 = $2800 (for both).
=> Same the price of Bitcoin in past week when reach $2900 before Bitcoin Cash listing to exchange
If you're implying that the following will be true in the immediate future after August 1: price(new BTC) + price(BCC) <= price(old BTC) . One implication of this inequality is that the rate at which BCC should fall should be theoretically equal to the rate of rise in BTC. If this was the only reason for market movements, one could say yeah this is possible, but there are many other factors at play which may invalidate the inequality.
There is just one short-term certainty: volatility.