I think there really shouldn’t be as much criticism of Cortana not having died at the end of Halo 4. It’s a knee jerk reaction and not really warranted.
For starters, we didn’t actually see Cortana die. If she can survive without her chip and she says pretty unambiguously that bits of her are still in the ship then how does that add up to her being dead? Plus, in escalation they point out that the Didact and bits of the Didacts ship are spewed out of slipspace. That means it’s fairly reasonable that Cortana could have survived long enough to reach the Domain where she could repair the damage done to her “physical” form.
Secondly, the Librarian discusses with the Chief about her plan for
him to assume the Mantle as the Reclaimer. She then says that “even your ancilla AI Cortana” is part of this plan. For me this was a massive hint that Cortana had not died in Halo 4. If this is the Reclaimer saga and presumably will end with Chief taking on the Mantle to save humanity; how can he do that without Cortana if she’s dead and part of that plan?
Thirdly, was I literally the only person who watched the E3 2013 trailer where he’s walking in the desert with Cortana’s chip and thought “oh, he’s on a quest to get her back”? How can she be dead if Chief is on a journey to find her? Yet the amount of outright denial in the run up to Halo 5 is really quite staggering given that trailer was out for so long.
343 planned the series as a trilogy. I find it extremely unlikely that they could change something as important as “Cortana becomes villain and tries to conquer Galaxy” on a whim as its a major plot point in Halo 5 and presumably Halo 6. This is why there are hints pointing to Cortana’s survival and having a larger role in the story in during Halo 4.
Okay, the main complaint is that this somehow cheapens the Chiefs personal development. That Cortana dying meant the Chief learnt about his humanity through having his bond with her broken. With all respect, how? He’s not going to revert or regress back into being an automaton. That’s why he takes it on himself to go after Cortana in 5, he feels responsible and doesn’t just take orders like a machine would. Like he tells Locke, he knows Cortana is a threat but she is his problem; nobody else’s. Cortana being alive hasn’t negatively affected the Chiefs character development. It allows them to follow up on and develop it further as it presents him with a very difficult personal problem.
The second thing is probably the most knee jerk reaction. That having Cortana come back cheapens her sacrifice. For example, some people say this about Gandalf in Lord of the Rings how he comes back exactly the same in a new colour robe. But, a key difference is that Cortana has very evidently changed and it is extremely unlikely that things can ever go back to the same. Even if she, for whatever reason, changes back to being a good person, she’s done so much damage that the UNSC will try to destroy her anyway; Chief can never have her back. Either he kills her, is forced apart from her, or goes against the UNSC to protect her if he manages to redeem her.
Bringing Cortana back has pushed the narrative forward and into a very interesting direction. I mean, where else could they have gone with Chiefs character? Chief can only discover his humanity if he has to let his personal feelings and sense of right and wrong come to the fore. But how can you tell a personal story like that if the only character chief had a personal relationship with is killed in the first act of your story? Not everyone has read the books and it would have felt very forced to put the emotional focus on Halsey or Blue Team in the 5th game. Indeed Blue Team completely wouldn’t suit that kind of story because a story about courage and military comradeship is to in Chiefs comfort zone as a “machine” super soldier. They could have maybe done something with Halsey; but I still think there’s a severe problem with her being an EU character.
The simple fact is that the Reclaimer Saga is the story of Chief and Cortana. 343 has obviously decided the best way to show Chiefs humanity is by focusing on the emotional drama between him and Cortana.