Now I know most of you probably already know that 343 said that the terminals in Halo CEA would give hints to the story in Halo 4. So I noticed that guilty spark calls the flood an ancient enemy and if you read the description for Halo 4 it says the chief faces an ancient evil that threatens the fate of the whole universe. Now those too things are pretty much the same now your probably thinking didn't MC kill the flood, yes but 343 once again said that the flood is almost impossible too completely wipe out since all you need is one parasite to infect a being and then they quickly multiply. Also if you ever watch a Halo4Follwer video he points out a squid looking thing on the ship, this could possibly be a flood parasite. Also 343 confirmed the planet being forunner so maybe there is still flood on it. Also there are still rings left so maybe they are somehow released again like maybe the chief does something on the planet he's on and he releases them. There are plenty more ways the flood can be alive.

I mentioned that the ancient evil threatens the face of the whole universe so maybe the flood completely outbreaks infecting by the millions. Also saying the entire universe meaning remaining covenant, elites, humans, forunners and precursors (if there still are any) could all be involved in the fight.

Another possibility and what most people are saying is that the enemy is the precursors now definitely ancient and I guess you can say evil. But if you read some of the books they say there is only one remaining, but they also said that they can travel to other galaxies so they probably have thousands of planets and would kinda be hard to kill. That being said they would've also survived when the halo rings fired. But them being an enemy the humans have too fight that would probably be impossible since they are so highly advanced in technology.

Well that's all I have for you today, let me know what you guys think in the comments.