Eliezar's entire indentity, both physically and religiously, had been changed by the concentration camps. He sees only "an image" of himself because he can no longer see the person he used to be. As he stares into the mirror, he sees the image of some emaciated person who he has never seen. In addition, all of his beliefs have been challenged, his family taken away from him and he can only look at an someone who vaguely resembles himself but looks more like he is "walking up from the long night." The inference is that he will have to take time to get to know himself again, through self-reflection and eating health food, something he has not been able to do since he had been forced to focus solely on survival.
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.