system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] How did Sargent Johnson survive both the destruction of the Halo and the detonation of the Pillar of Autumn?

And how did, of all things, 343 Guilty Spark kill him if those events didn't?
gpt
Johnson was immune to the Flood from his Orion Project modifications that were the basis for all the future Spartan programs. Once he survived the Flood he evacuated onto a Pelican with a few more Marines and a pilot. They all hid on the nearby moon. So Johnson was nowhere near Halo when it was destroyed.

As for Spark killing him, that was a Forerunner directed energy weapon that. You don't usually survive shots from those without a little help.