I have been looking into known deaths not seen in halo games and movies. Cortana is truly dead and Sarah Palmer is correct about the rampant Cortana is what survived. There isn't any info released on the Cortana we see in halo 5 except seen under related info of warden eternals page. Alpha Niner from odst lived on to be integrated into the Spartan IV program. Dare is somewhere and unknown where. We all know where Buck is. Romeo is in a different Spartan team then Buck. Dutch retired and lives with his wife. As for The Rookie and Mickey, The end of the covenant war revived the insurrection or rebels. All of alpha nine ran an op and it turned south, Rookie was executed, his killer defeated and executed by Dutch, but later in the op Mickey turned on alpha nine, out of the mental state that you have when you loose someone right next to you that you have known for a very long time, when your lost. Mickey is now serving time for his betrayal to the UNSC. Dutch retired shortly before the funeral held for the Rookie. April Orenski is someone I have not been able to track but she's alive, or missing or hidden. Sully became a commander and is directing section 2 of ONI and is able to access some information on the Master Chief. And Captin Laskey is still the CO of the UNSC INFINITY. Those are all of the ones I researched. However there is one that I find curious. A forerunner AI that was corrupted by the Flood that was on the ARK and tried to pay for his crimes by siding with the humans against the Flood or something. I am curious about it and it remains missing. Another thing is that the Guardians were never made for the encounter with the Flood. They were kinda like the Ultimate level of Forerunner authority. Mostly as a symbol and small hammer instead of a nuke. The way rampant Cortana is using them is a major complete abuse. Just my opinion.