Some media are indicating that Apple will abandon the sale and support of music and videos after the elimination of iTunes in macOS Catalina. Remember that the 10.15 version of macOS will have applications independently of Music and Apple TV.
But this is far from the truth and also does not make sense. Apple will continue with audiovisual sales, despite boosting its streaming video content service in the coming months. On the other hand, the Apple Music service does not stop gaining followers by having a perfect sync between music platform and Siri.
Recall that the WWDC 2019 held a few hours ago, iOS will receive a function that will allow stream the music we listen to to another iOS device and this in turn play it on a speaker or on the AirPods or any other headset. Therefore this it's not the end of iTunes as a content store, which will remain fully operational in each of the segregated applications.
On the other hand, the content export will be migrated to new applications without great effort. Therefore, it is not true that purchased songs or movies may be lost. The files will be migrated to a different location, but knowing how Apple prepares it, most users will not encounter any problems with the migration.
The only drawback for the user is the adaptation period to new applications. Until now, everything was in the same application, and you just had to select the tab corresponding to the desired service. Now you must think that you have to open another application, but this will be more adapted to the content you want to reproduce. At the moment we do not know functions that disappear. Just some logical changes because where they go makes more sense of being. For example, the option of «Share at Home» you are now in the sharing options in System Preferences in macOS Catalina.