Fortnite was removed from Apple's App Store last month after legal issues over in-app payment method arose between Epic Games and Apple. Last week, Apple terminated Epic's developer account which has made it impossible to reinstall Epic's iOS apps.
Users that already have the Fortnite app installed in their iOS devices can play the game and install update files. However, they wouldn't have access to the latest content of the game that comes with the launch of Chapter 2: Season 4, and are unable to use crossplay with other systems.
Before Apple terminated Epic's account, there was a way to reinstall the game for those players who had downloaded Fortnite some time in the past, at least once, and later removed it.
The method simply worked by visiting the My Purchases section of the App Store and tapping on 'purchased' and then 'my purchases'. This would display the app directory of all iOS apps that an iOS user would have ever downloaded. The user could then search for Fortnite and tap on the cloud icon to download it. This trick could work even if a member of an Apple Family Sharing plan ever downloaded the app on their iOS device in the past. Downloading Fortnite through this way would have also installed about 10GB collection of Epic app files.
Similarly, after Flappy Birds' creator pulled the app from the App Store, users could still play it using the same trick, until the game stopped functioning after Apple launched iOS 11 which didn't support 32-bit apps.
As a result of the termination of Epic's developer account, the company is neither able to submit new apps to the App Store nor issue updates to the existing ones. And now as its apps are completely delisted, they can't be reinstalled even from the purchase history.
Epic has not yet commented over Apple's move and we do not know whether it will give up and eventually comply with Apple's demands for in-app payment method or not.