- last post: 01.01.0001 12:00 AM PDT
Because he probably has some sort of super secret Forerunner shield technology that we don't understand.
ORRRRR
Considering he's important for the plot, you can't kill him or it wouldn't make sense later on. That's why Sarge and Half-Jaw are invincible, because they are crucial characters throughout campaign mode. In Halo: CE, it made no sense that you could kill Sergeant Johnson in almost every level and have him reappear over and over and over.
Or the super shield thing.
I could be right.
Or wrong.
Or not.
Or who gives a blam?