What happens if you delete a game from your PS4 library?
You should be able to re-download the game via the PlayStation Store. Search for the title that you deleted in the store and it should show that it can be downloaded. If it doesn't tell you you can download the game, contact PlayStation support and they will sort it out for you. Alternatively, you can also go to your games library and travel to the Purchased tab. It should show every game you've purchased on that PSN and allow you to reinstall.