That's why it's lost.
18.2a: "(1) When Ball Is Lost. A ball is lost if not found in three minutes after the player or his or her caddie begins to search for it."
Definition of "Lost":
So, you didn't find the ball @Sandy Lie. It's lost.
I think that if you saw the ball go into the sod face, but it's too deep to retrieve it, it is virtually certain where it is: embedded in the sod face (which is not part of the bunker, and is not sand), and as such get relief under the embedded ball rule (16.3), but I don't know where the relief reference point is since you don't really know the position of the ball, and yet you can't set it closer to the hole than the ball was. In fact, depending on the shape of the bunker in reference to the hole, there may be no place to drop, so an unplayable (from the point of origin, i.e. same as lost ball) might be the proper course of action. I don't know... Good question!