I really don't know where I stand with this. On one side, I think the death of Cortana is a good thing. Master Chief has always seemed to be a pretty emotionless and machine-like person, but with the death of Cortana, maybe it will help him to realise that he is more than that, maybe this new trilogy of games will focus on loss and discovering who you really are.
But then again, I don't see how they can kill her off either. She's an important character to the series, and was instrumental to saving the galaxy along with MC. How would he have deactivated the Halo rings without her? And what if a similar situation arises in future games? From everything that I've read so far, I reckon she will come back either at the end of Halo 5 or the beginning of Halo 6, but not the way we all remembered her as.....