The Ending? (spoilers)

First of all, I really liked this movie a lot. But the ending was a bit confusing for me, perhaps I missed something? Did Georgia die? They were never found, but the security guard saw them for a moment and had a heart attack, and you could hear them giggling, but was that just a paranoid delusion, or were both girls really there? If Georgia died, I don't think she'd trust Virginia very much after stabbing her in the back like that.