My opinion, keep cortana dead till one of the said theories is used on her revival is shown say 2/5 or 3/5 through halo 5 and the game continues from there with the ending showing her return and we move on to halo 6 or rather keep halo 5 cortana free and in the ending show some form of her appearance in the ending and have halo 6 focused on getting her back which in the end he does. Sounds about right to me. Just a rough general plot line, nth too in depth with whatever enemies needed to be made and introduce done as usual. Dont see what new enemy he can face now besides the didact returning in some fashion or betrayal (highly doubtful).
