I think digital restorations do exist real since quite some time - with Photoshop. However I cannot name any literature on this.
But the real restorers are doing quite a good job, too.
I mean a digital restoration is not really optimal - sometimes, when there is no money to do a real restoration, they are better than nothing.
Often, they are also part of a real resturation, as a kind of preparation. Resturations - digital or not - are always an interpretation.