Brace yourselves: there are TWO different endings to Great Expectations. We know, we know. See, Dickens originally wrote a kind of downer of an ending, the kind that would have premiered at the Sundance Film Festival, where his protagonist doesn't get the girl in the end. Pip and Estella reunite after many years, and Estella isn't the bright star she once was. She was married to an abusive husband who died, and now she's married to a poor doctor. Pip isn't jonesingfor her anymore. They part peacefully, but as strangers. The end.
One of Dickens' friends—who, exactly, scholars can't decide, but definitely a fellow writer—gently suggested that maybe the public would like a different kind of ending: the kind that would premier in the Chinese Theater in Hollywood. Because Great Expectations was serialized, Dickens was writing his "episodes" several weeks in advance. He took his friend's advice and rewrote his ending in a way that suggests that Pip and Estella will be together, but he did it in a way that preserves the original ending's melancholy and uncertainty.
Pip returns to Satis House to find that it has been torn down, but on the horizon he sees a figure that looks a lot like Estella. In fact, it is Estella: out of the rubble comes new love. It's a very phoenix-like moment.
But the mists also come. Pip says, "I saw no shadow of another parting from her" (59.46), and we are led to believe that Pip and Estella live happily ever after. But notice that they're not exactly riding off into the sunset? Pip still mentions it in the negative—not light, just "no shadow." We like to think that in appeasing the masses with this second ending, Dickens infused it with the subterranean undercurrent of another meaning altogether.