As you already know, if you know the app that was deleted then it is easy to either download it from the App Store again or restore it from the App Library. The App Library is the last Home Screen when you continue to Swipe Left until you reach it.
If you do not remember which App was deleted, then things can get difficult especially if you do not have anything to use as a reference. My recommendation is that you take screenshots of the Home Screens so that you have something to refer to if an app is deleted by mistake again.
The other option is to create and have regular backups of the iPhone. You can backup either on iCloud or on a computer. You can always restore your iPhone from the last backup and that would bring back all the apps that were on the iPhone. This method is time consuming but can get you out of a bind and recover a deleted app and its associated data.
Axel F.