Seriously? You guys think Cortana is gone for good? Get real bro. Cortana is literally engrained in the Halo story. She is too big of a character to be just let go for the sake of a story. She was part of the whole thing. In my opinion, I'm almost positive she will come back. It has been rumored that she will return as a human. How, why, when, and where? I haven't the slightest idea. It may not be in the 5th game, but mark my words, she will be back.