User blog comment:James12708/Reapers VS. Forerunners VS. Angels from Darksiders VS. Humanity from Halo VS. Council and humanity from Mass Effect VS. Imperium of Man/@comment-5436239-20130130074424/@comment-4721065-20130130103624

Please go to the second page of the blog comments where it's brought up that Halo Rings only destroy the nervous system, leaving lesser organics alive. Therefore, if Reapers use computer wires or whatever instead of nerves, they would survive the Halo. Of course, they would never make enough of a threat to warrant the Halo Rings' deployment, but that's another story.

Also, on that second page, it is pretty much universally agreed upon that any WH40K faction (particularly the IoM) would be the not-so-distant second, mainly because Games Workshop writers still have a certain semblance of realism and understand that having factions with infinite resources is boring.