One of the reasons I have more confidence in React than Angular is that Facebook and Instagram actually use React in flagship products. I wouldn't worry about React abandoning the web until Facebook and Instagram stop using it for their web products.
Also, while all Dart does for Angular is fragment the community (because now we have Angular web devs using Dart, Angular web devs using JS and soon Angular web devs using AtScript), React Native actually does the opposite.
A lot of web devs already also do mobile development or at least work on hybrid apps (i.e. WebView-based mobile apps). React Native enables web devs to develop mobile apps that wouldn't have been feasible before (either because of the limitations of WebView or because they would have had to worry about learning an entirely different stack that is orthogonal to their web technology knowledge).
Also, while all Dart does for Angular is fragment the community (because now we have Angular web devs using Dart, Angular web devs using JS and soon Angular web devs using AtScript), React Native actually does the opposite.
A lot of web devs already also do mobile development or at least work on hybrid apps (i.e. WebView-based mobile apps). React Native enables web devs to develop mobile apps that wouldn't have been feasible before (either because of the limitations of WebView or because they would have had to worry about learning an entirely different stack that is orthogonal to their web technology knowledge).