I finished solo Legendary a few hours ago. We’re left not really knowing what becomes of Cortana. Does she fade into nothingness or what? My thoughts:
343 thinks that fighting the Covenant is so vital to Halo, it has to come back in this trilogy even though it makes no sense in the canon. Yeah, the books explain why, the they explain why because 343 wanted the Covenant to be enemies in the games, not the other way around. Even that they won’t let go of. What’s the two most important parts of Halo? The Chief and Cortana. If they can’t even let go of humans versus Covenant, there’s no way they’re letting go of Cortana, especially this early in the series.
At the end of Halo 4, although Cortana had lost most of her data, and presumable her chip, she was still intact. And it is clear she doesn’t need a chip, since she can move throughout networks. What comes after rampancy? Metastability. And that’s when an AI is said to be a full person. If any AI can achieve that, it’s Cortana. And if she’s metastable, does she even need a network, or has she transcended that? She certainly seemed to have transcendede that at the end of Halo 4. And perhaps this concept is also related to what the Truth And Reconciliation’s AI meant when it said it would be free (CEA terminal). And Cortana was clearly still intact, but had lost most of her data. What causes rampancy? Too much data. Too much thought. If she lost all that data, it’s the AI equivilent of anti-aging. Sure, this might go against the metastable theory, but perhaps losing the data which causes rampancy is part of the process to achieving metastability. And not to mention Cortana was more powerful than ever before at the end of Halo 4, surely a mere nuclear explosion couldn’t defeat her.
And if my theory is correct, perhaps the Forerunner technology which aimed to achieve immortality will be used for Cortana, so she’ll get a physical body (robotic, but still be far more real than, say, Spark).
As for how she escapes the nuclear explosion, either she manages it herself, or perhaps the Librarian rescues her, and maybe even (if she still relies on networks and computer chips) transfers her into either a Forerunner network (temporarily) or a body like I described in the previous paragraph.
And if she does get her own body, maybe she can take tissue from Halsey (sort of like what was stated as a possible way of saving her from rampancy in the earlier levels of Halo 4) to make it biomechanical, or even biological.
Cortana will come back… we’ll just have to wait to see how.