[quote]did the humans actually have a way to beat/cure the Flood, or did the Flood just leave them be?[/quote]That's a debated topic in the lore community. I personally stand by what the Primordial said, that there is no cure, and the Flood chose not to infect humanity. However, it does beg the question of why the Primordial was doing such extensive and horrible tests and experiments on humanity on Zeta Halo. [quote]Also, if the Flood just chose to retreat and leave the humans be, do we know the reason?[/quote]It was done to bait the Forerunners into preserving humanity, and dooming themselves.