Deleting the app deletes the files inside, and losing the devices would mean the files are lost as they are not stored on our servers. It would only be possible to get your files back if you use iCloud Backup on your phone or have manually backed up your phone to your computer. Then you can restore a backup from before the time you deleted the app. Here are instructions from Apple on how to do that.
Note: There was a feature in Locker 3.0 and earlier for premium users to manually backup individual files to their iCloud. If you backed up a file(s) to your iCloud, they will be restored automatically in Locker 4.0+. The app will check for any available files to be restored when the app opens.