You'll still be able to buy music from the store on Mac, iOS, PC and Apple TV. Plus, you can still use your iTunes gift cards or credits with new apps. Meanwhile, the new TV app will contain all the movies and TV shows that you have purchased or rented from iTunes – in the future you can buy or rent out the application itself.
All your podcasts will live in a new app for announcements, of course, while your audio books will make their way to the updated Apple Books application. You will also be able to purchase audio books from the Books application. Finally, the ability to back up, update, and synchronize iPhones, iPads and iPods will move to Finder. Apple says it will be easier for you to retrieve and play files on your devices and that your previous back windows through iTunes will not be affected after being updated in Catalina.