Analysis: What's Up With the Ending?
The obvious answer to this question is: Ligeia somehow manages – through force of will, perhaps – to inhabit the dead body of Lady Rowena, transform it into her own image, and then reveal herself to the narrator.
Unfortunately, the "obvious" answer is also the craziest. For one thing, you have to notice the "somehow" up there. There's no logical explanation for how Ligeia possesses Lady Rowena's body – or for how the "brilliant and ruby colored fluid" falls into Rowena's wine, or for pretty much everything else (24). It doesn't help that our narrator is high on "an immoderate dose of opium" the whole time, and that he's constructed a funhouse/madhouse of a bedroom for Rowena (23). All of these many, many factors make any kind of interpretation really complicated. So maybe the narrator does stare into "the full, and the black, and the wild eyes" of Ligeia. Or maybe he's just hallucinating, and his desire to have Ligeia back leads him to imagine the whole, strange resurrection scene.
Does that leave us to choose a "correct" version of the story? No. But we should keep in mind two very important parts from earlier in the tale. On one hand, the Glanvill quote about the death-conquering power of, well, willpower. On the other hand, though, we have to remember Ligeia's own "conqueror," the worm (you can read more about him and his story in "Symbols, Imagery, Allegory"). In the poem – which, mind you, she composes – the worm is the hero, and wins out over all. Which is the true champion this time around? We'll let you decide.