If asking about employment opportunities, native will never die out. There will always be opportunity for work in native mobile applications. There are also many advantages of using native over cross platform such as always having access to the latest APIs and developer libraries that may not be available to cross-platform without some native development involved or can wait until someone develops a bridge for you.
If you are asking about what you should develop with first? It really depends. React-Native is great for building proto-types or basic MVP application that doesn't require any of the latest and greatest features Apple has to offer at the moment. But if you're asking what to learn? I would say native will always give you a larger advantage as it will give you a good foundation in mobile development and provide you access to the latest native libraries. It is also a useful skill that can give you an edge in cross-platform mobile like react-native because you will most definitely encounter a situation where you will have to go down to the to native side to extend functionality or utilize APIs that are not yet out of the box.