meh, I agree that would be a great way for the story to go but I still need cortana back at some point in halo 5/6 or i will have to go to 343 industries myself and complain until they give in and add her back or I will have to somehow buy the rights to a halo game just to add her back (I would, don't doubt me)
I would be fine with him having another companion throughout halo 5 but at some point maybe in the end they need to bring her back, I mean if they put it at the end it would keep the feeling of the moment at the end of halo 4 but satisfy many of the fans...