Things you're sacrificing when going away from React:
1. Stability. FB uses it for their main product, which is probably the biggest web app of them all, they pay many devs to work fulltime on it. People coming from Angular, who had to migrate all those breaking changes over the years know the struggle.
2. Options like React-Native, React-VR and co. React enables your devs to acquire a whole new range of possibilities. It isn't just a web framework.
Options like React-Native
It's difficult to convert a React web app into a React Native app, but you can use many React Native components on the web (via react-native-web. [1]) In other words, you can't run a web app on mobile, but you can run a mobile app on the web.
I just launched a little game that I built with React Native [2], where I have a single codebase that supports iOS, Android, Windows, and web.