I don’t necessarily believe in this 100% but I was thinking about it today and there is one possible way she survived. In the scene where her copies attack the Ur-Didact there are maybe four or five Cortana Copies there, yet only two or three of them actually hold him down. Then two are seen impacting his armor and disappearing and one is specifically shown impacting his helmet.
So what if a piece, or more, of her survives because she stowed away on the Ur-Didact’s armor?
This leaves us with, “why would she do that?” Well I don’t know why she would do that, but we also don’t know what the Librarian did to her. Maybe the Librarian wanted her to get in touch with the other Forerunner somehow and this is how she chose to do it? The Epilogue suggests that the Ur-Didact is now in the custody of living Forerunner, so this could mean Cortana is as well.
I’m just speculating here and for all we know she could definitely be 100% dead, but there is nothing wrong with speculation. It’s just a thought.
I think there are a number of plausible ways for Cortana to return:
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Didact armour, as you say.
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Librarian backup.
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Monitor promotion.
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Halsey backup or restoration.
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Mendicant Bias.
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Unknown Forerunner systems from Requiem, Didact’s ship, Domain etc.
That’s sort of assuming she can transfer from hardlight to dataport. It also assumes it happens by accident, as why wouldn’t cortana tell chief this?
> That’s sort of assuming she can transfer from hardlight to dataport. It also assumes it happens by accident, as why wouldn’t cortana tell chief this?
If the Librarian backed her up then she could easily muzzle her or have her inactive for example. Further when Cortana is copying herself they can’t just magically communicate.
The Cortana version at the end may simply not be aware of another backup version or even replicated version’s progress past Rampancy etc.
It’s an interesting story arc that I’m enjoying immensely though.
If the Librarian backed her up, you’d have to wonder where she went from there. Requiem and the Librarian AI are toast now.
> If the Librarian backed her up, you’d have to wonder where she went from there. Requiem and the Librarian AI are toast now.
“Yes! I have a duplicate of Cortana! Now the story can proceed as planned and Master Chief can save the univer-is it just me or is it getting rather toasty in here? Wait you can’t just BLOW UP Requi-”
Fortunately, Requiem did not blow up. It was tossed in a sun.
> > If the Librarian backed her up, you’d have to wonder where she went from there. Requiem and the Librarian AI are toast now.
>
> “Yes! I have a duplicate of Cortana! Now the story can proceed as planned and Master Chief can save the univer-is it just me or is it getting rather toasty in here? Wait you can’t just BLOW UP Requi-”
> Fortunately, Requiem did not blow up. <mark>It was tossed in a sun.</mark>
Which then blew up. In a supernova. Destroying Requiem.
However, the Librarian easily could have uploaded herself to “The Absolute Record” So we may have not seen the last of her.
We haven’t seen the last of her, there’s no way that Halo 5 and 6 can have her absent.