[Alex Murphy]

Or does it refer to people who deny God? Will those who deny God exists, the saints exist, etc. be annihilated?

I have no doubt that the author was referring to the heretical belief known as "soul annihilation". It teaches that the soul does not survive death, and therefore does not experience Hell (and depending on the teacher, it may not experience Heaven, either). Jehovah's Witnesses are IMO probably the best known adherents of soul annihilation.

Related threads:
Theologian Jim Cronfel Addresses Systematic Annihilationism in His New Book "Eternal Christianity"
Pope says hell and damnation are real and eternal
HELL: Eternal Torment or Complete Annihilation?

[Salvation]

I think you are talking about “annihilationsim” which is a very strange belief in no hell......so I would construe then......no heaven either.