What is the significance of the book’s final image, Wiesel’s face, reflected in a mirror?He writes that a corpse gazed back at him, with a look...

Look at your question's clarification : "He writes that a corpse gazed back at him, with a look that has never left him."  Please note that the final sentence never says that Elie sees himself--nor does he see a corpse.  In the last line, the corpse is the subject of the sentence, the corpse controls all vision, the corpse's eyes contain "the look"; the corpse's eyes "gazed." 

So the ending suggests that Elie does not and never will see himself.  Also, the ending presents no evidence that any "aspects were born in their place." 

And "not one thought of revenge" but only bread--undercuts the "liberated" idea--man is not free, and moral reflection is meaningless; man's moral worth is based on his existence, so existence is the only moral concern.  Then read on to the last line--Night offers no hope.