Good idea; however, there is one problem with your post. If it was all like save cortana, destroy the flood, it would not
feel right, it would be like your doing Halo 3's campaign over again. So I think, like Halo 4, it was totally different to
the previous game which was in the trilogy. That's what I think Halo 5 should be, a totally new story what still fits in with halo.
PS: I still would like the flood in Halo 5.