According to me, it doesn't look like his one eye is actually missing. There isn't really a definite way to tell though. Could you try gently wiping at his possibly sealed eye with a cotton swab? Make sure you hold him quite firmly while you do that so as not to cause him any more harm if he moves.

As for the eye that is out of its socket, I doubt it will ever be able to function again. :/ You could try cleaning up around it to prevent infection.