Here is a new blog update from Halo Archive
Halo 4 had a dramatic impact on the lore community with a formal introduction of a living Forerunner not only that,The Didact himself. The final journey of Chief and Cortana had the pair hunting Didact down throughout his Requiem fortress to a final showdown above Earth itself. While all three combatants would survive the encounter separate paths were drawn sending the trio on their own ways. Halo 5 has Cortana return from her seemingly assured death, new in form, with radical ideas to match. Frankie and Cortana insist nothing has changed about the AI yet we see stark differences with her behavior and willingness to sacrifice not just one person but entire planets for her goals. The intention of this article is to clear up how Cortana survived and the eeriness of her current state, one i feel may be imposed upon her..