MAJOR CAMPAIGN SPOILERS AHEAD, DO NOT CONTINUE IF YOU HAVE NOT FINISHED HALO 4.
Ok, so personally, I hate the idea that Cortana is dead and gone as she is my favorite character, followed very closely by the chief. Although, I have done lots of research and have concluded (in my mind) that we will see her again. Perhaps towards the end of Halo 5 or beginning of Halo 6.
Note: Yes I know this theory has already probably been theorized, I just needed to get it off my chest, because as I said, I hate the idea Cortana is gone.
For one, 343i left her “death” very open, she never says goodbye, she never says she’ll never see us again. What she does say is “most of me’s down there.” Now, where is “down there.” If you recall, in the last mission (Midnight) when you first see the Didact inside the shield within the Composer, Cortana says, “Activity, significant slipspace event building under the composer!” That is what the swirling orange pool under the Didact/Composer. I also believe that is what Cortana is referring to when she says “most of me’s down there.” Now, all of her data was located in the Didact’s ship’s systems (Chief inserted her into the third pedestal, she splits herself for the third time, Didact obliterates the pedestal). We know this because how else could she use hardlight to make a bridge to the center of the Composer where the Didact is? After chief detonates the nuke, the Didact’s ship is blown to smithereens and Cortana protects chief in a hardlight shield, where she makes her “most of me’s down there” statement." After she vanishes, you see hunks of the Didact’s ship falling down… down where? I think falling into the slipspace event, the same slipspace event the Didact fell into. Most of Cortana was in the Didact’s ship’s systems. Most of Didact’s ship was sucked into the slipspace event before it collapsed, therefore Cortana is in slipspace.
Now, the part 2 of my theory. There is another theory, theorized by Dr. Catherine Halsey, that AI’s can acquire unlimited storage space within slipspace. Sources: Halsey’s personal journal, Halo Reach data pad #17. Keep in mind that this is a THEORY of Halsey’s, therefore not proven. But who better to put it to the test than Cortana. So, if this is true, then Cortana would no longer need a physical storage container. No one can really understand how this works since it’s just a theory, but my guess is she’ll be able to do all she could do before and more, without the need for being physically inserted. Maybe she can flit parts of herself in and out of her new, infinite slipspace container, I don’t know, my guess is we’ll see this in Halo 5 or 6.
How does this tie into the future of the franchise? 343i has stated that Halo 5will be the darkest game of the new trilogy. This doesn’t seem to fit with the return of Cortana in Halo 5. So, either Cortana doesn’t come back until Halo 6, or she comes back in Halo 5, but in a fully rampant state. When Cortana split herself into the Didact’s ship, she split her “rampant parts” into the system, therefore it is her rampant parts that went into her new slipspace container. The lifesize Cortana you see in the hardlight shield, the one that saved chief, is the last bit of Cortana that wasn’t rampant. That part of her I believe is gone for good. But her rampant parts are alive and well… well and rampant… in slipspace. Now, what could be darker in Halo 5 than the return of a fully rampant Cortana that wants to kill her closest ally, the chief? I’ll tell you what, the return of a fully rampant Cortana that wants to kill the chief and is sided with the Didact! The Didact and Cortana fell into the same slipspace event. Didact was in his full armor when he fell in. We don’t know the capabilities of Didact’s armor and whether they could withstand slipspace, but I’m going on the assumption they can. So, to make it even darker, we all know the Flood is going to turn up again sooner or later. And I believe this is what the Librarian is referring to before she was so rudely interrupted by the Didact. I’m talking about the point where chief meets the Librarian at the end of Halo 4’s 5th mission (Reclaimer), where she is saying that she planted seeds in the human gene pool that would lead to the Spartan program, Mjolnir armor, and Cortana. She says that, “you are the culmination of a thousand lifetimes of planning,” to which chief responds, “planning for what?” Then the Didact interrupts and the Librarian doesn’t get a chance to finish her thought. I believe she knew the Flood would return soon and the chief would be vital to taking it down, again. What could be darker in Halo 5 than the return of the Didact, the return of the Flood, and the return of a rampant Cortana???
Additional thoughts:
Some might argue if the Librarian knew so much, why didn’t she help when the Flood attacked Earth in Halo 3? I think she knew the chief and Cortana could handle that small outbreak of Flood on their own. Notice I say that was a “small outbreak.” Specifically it was the Gravemind from installation 05 the took over High Charity and made its way to Earth. It’s been confirmed that no one knows where the Flood originated, one theory is the Precursors made them to seek revenge on the Forerunners. Could this be the Didact’s motive? He and his Prometheans failed to obliterate humanity in Halo 4, so maybe he reintroduces the Flood in Halo 5 to completely eradicate humanity once and for all? How would he do this? I don’t know, it’s just a theory. I think it’s safe to say that if the Flood returns in Halo 5, we’ll see them obliterated once and for all in Halo 6. That would assume we found out where the Flood “lives.” In other words, what part of the galaxy they reside in. Maybe the Flood has a singular entity commanding it, similar to the concept of a Gravemind, but on a whole new level. Maybe they have a home planet that must be destroyed. Or maybe, since humanity is confirmed to be seeking out the remaining Halo rings, they just need to find where the Flood lives, find out a way to get a Halo ring there and activate it, followed by a crazy escape scene involving a certain guy in a green suit and a warthog.
Personally, I’d really like it 343i took the story along these lines. I know many of you HATE the idea of the return of the Flood. But, you have to admit it’s inevitable, at some point they WILL return, whether it be in the Reclaimer trilogy, or some other future series. I’d particularly like it if I were right about what will happen with Cortana. As I have said, I don’t want her to be gone forever!
Remember, this is just a theory, so please be nice!