So. As a new member of the forums. I wanna do something "Big". Make a Theory. See what the Community says about it.
BTW: This never really came to mind until I saw Halo Followers videos about the flood.
So, I'm pretty sure we ALL know what the Flood is. It is a terrifying, its a Hivemind full of alien beings. I won't get into full detail as of now.
With the legendary ending cut scene to Halo's game " Halo 5: Guardians ". It shows a ring orbiting a planet with Cortana humming a tune in the background. But how does this relate to the Flood you might ask. Well. Hear me out.
Near the end for only a split second. You can hear a sort of screech that comes on when the Halo Rings lights were activating. " But Poppy. Its just the sound of it turning on." That MIGHT be the case. But. When you listen to it very closely for a couple of times. Then you listen to flood sounds from the early Halo games. It sounds almost similar. If not, Identical. (Maybe not identical).
With the Halo comic book. "Halo:Escalations" There were Flood occupying the ship "Spirit of fire" it is also the ship from Halo Wars. Note that this was after the events of Halo 3. So. Theres the proof that the Flood was still alive even after Halo 3. It is also known for the Forerunners to keep the flood in containment for various reasons.
Also note that since Cortana has control of the Forerunners, She may know where these flood beings are and may have intentions to use them.
That is why I. PoPScotchXx, thinks that the flood will be in Halo 6. And hope near and dear to my heart that the Flood WILL return. Please excuse me if I made any mistakes in spelling.
*ADDED CONTENT*
So after i made some researching. Halo:4 - 7 is the reclaimer Saga. Right? This means that humanity has to take the threshold of the forerunners. correct me if I'm wrong,but. as i noted earlier, there were numerous reason for the forerunners to have the Flood in containment, in order for the humans to take the forerunners threshold, they need to take/destroy the rings right? Thus supporting my theory of the Flood returning.
imagine this. You and Blue Team walk into a forerunner structure of a sort only to find dead Grunts,Jackals,Elites, as well as Hunters, whilst there are numerous marine body scattered about. some of the bodies, you noticed blood that leads into a room. You activate the control console next to the door of the room. but before you do, you hear a screech, a loud,ominous,terrifying,ear drum busting, screech. your body shakes in fear as you remember that screech and the memories of it.
You continue to open the door. Only to find hundred if not thousands of flood forms of all types. and behind them, a huge chunk of yellow/greyish flesh. it looks all too familiar. You know what it is? yes, a gravemind.
doesn't this sound like it has to be in the next Halo game? let me know in the comments below.