There are 453 contributors to bitcoin repository on github, and they are free to contribute to whatever other projects they want. It's quite possible that some of them will contribute or already contributed to Bcash. But if by "Core developers" you mean people like Greg Maxwell, Wladimir J. van der Laan, Luke Dashjr, than the answer is no - they have their own vision, and they will be working on it no matter what is the price and hashpower of Bitcoin and its forks.