I think he will have those flash backs kinda like halo 3. she probly got partially into the didact,but at the end of halo 5 guardians should be the ending cutscene on an AI console halsey should plug in a chip while chief is watching and you see the light flickering about to show the Ai and th egame ends #MajorTease then they could make halo 5 precurssors
Her coming back would be cliched to say the least. She left Chief with a lot of valuable insight in Halo 4: "Before this is all over, promise you'll figure out which one of us is the machine." Having her return would negate any emotional aspect of Halo 4's ending cutscene. Cortana's role ended with her showing Chief that he is not just some blind automaton created to carry out orders.