RHEL and CentOS are aimed towards enterprise customers, Fedora is for individual users. I don't think there's any kind of real competition or even overlap between CentOS and Fedora. In addition, Fedora is basically a community project (although led by RH). It seems unlikely that RH would be able to shut down or materially alter the Fedora project even if the wanted to. In the worst case scenario the community could just branch the code and form a new organisation to lead its development.