system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Why did the Forerunners keep a sample of the flood on the Halo Rings? Why didn't the Forerunners program the Halo Rings to self destruct once the Halos fired? 

I think a more sane option would be:

Do NOT keep any sample of the Flood.
Program the Halo Rings to self-destruct after firing, since the Flood is suppose to be extinct after.
gpt
IIRC, the flood were kept on the Halos for research. Killing goddamn near everything to defeat your oppenent is a bit of a last straw. Allowing the Flood to be contained and researched allows for better ways to fight the Flood.