ComiXology recommends that their users back up their purchases through their ComiXology account and to download the new app to continue reading. However, the current app will still allow users to download and read their current books for a limited time. The Marvel and DC Comics apps, which are powered by ComiXology, appear to be unaffected.
In 2011, Amazon updated its Kindle app to remove the ability to purchase books from within the app to avoid Apple's in-app subscription and purchases policy, which requires developers to give Apple 30 percent of however much they earn. In contrast, Beats updated its app with in-app subscriptions in an effort to increase subscription sign-ups.
The new app, Comics - Read Comic Books and Graphic Novels by comiXology is a universal app that's available in the App Store for free. [Direct Link]