"Not sure what happens if you don't have the app installed - does it ask you to download the app instead?" FWIW Apple handles this by preinstalling and not all

"Not sure what happens if you don't have the app installed - does it ask you to download the app instead?" FWIW Apple handles this by preinstalling and not allowing you to remove the YouTube app. For other use cases there are a couple of ad-hoc systems that guide you to the App Store, namely a Game Center invite for a game that's not installed and plugging in an accessory that has a companion app that's not installed.