In a verbal bombshell that will rock the very foundations of your soul, Halo franchise development director Frank O'Connor let slip this amazing quote:
"I doubt we have seen the last of Master Chief."
This quote leaves open the possibility of another sequel to Halo!! I'll go out on a limb here and predict Halo 4, 5 and 6. In fact, I predict Halo sequels will continue to be released until people stop buying them. I'm psychic like that.