I does appear to have gone missing in the US App Store (as of 2022-03-12). I am unaware of any Symbolic Sound announcement. Perhaps an App Store glitch?
Regardless, discontinued apps are available for download as long as the developer has not explicitly deleted them, and has an active paid Apple Developer account. Deleting an app is a drastic step that is not the same as removing it from sale. If an app has been removed from sale it is still available to accounts that previously purchased. It will show in the "My Purchases" list in the App Store app. You can use that to see if there is a more recent update compatible with your iPad. Also remember that iPad-only apps will not show on the iPhone App Store and vice versa. Only universal apps show on both types of devices.
The most recent version of Kyma Control that I have shows version 1.5.2 (January 1, 2022).