Concerning the Flood's survival
Well, been a Halo fan for about 10 years, played all the games several times, have read most of the books(most importantly just finished the Forerunner saga)... I still don't understand, really, how the Flood survives into the present(future I guess - 2552). Cortana claims Halo doesn't kill them, it kills their food. Silentium seems to suggest they do kill the Flood(along with almost all other life). Why is there still Flood on the installations? Are they safe havens, like shield worlds? I know they're referred to as Fortress Worlds at some point. Did the Forerunner really think it was a good idea to keep samples around after how much of their civilization was destroyed? Perhaps unwilling to commit genocide? The creation of the rings seems to strongly suggest otherwise... I know they do reseed the galaxy with many species though. Why is there a Gravemind on Installation 05?