My Garage Band App was deleted and I lost all my files. Can they be recovered?
My Garage Band app was accidentally deleted from my iPad. Are the recordings I made still somewhere on my iPad?
When you delete the GarageBand.app you delete the projects as well from your device. Try to restore the projects by restoring the iPad from a backup you made before GarageBand got deleted.
See: How to back up your devices using iCloud or iTunes - Apple Support
Projects, that you saved in iCloud may still be there. Check the "My Songs" view.