The Collaborative International Dictionary
Destructionist \De*struc"tion*ist\, n.
One who delights in destroying that which is valuable; one whose principles and influence tend to destroy existing institutions; a destructive.
(Theol.) One who believes in the final destruction or complete annihilation of the wicked; -- called also annihilationist.
--Shipley.
Wiktionary
n. A person who believes that eternal punishment is the annihilation of both the body and the soul
Usage examples of "annihilationist".
The two last are said elsewhere to be directed against two sets of thinkers called the Eternalists and the Annihilationists, who held respectively the everlasting-life-heresy and the let-us-eat-and-drink-for-tomorrow-we-die-heresy.
Somehow word of the importation of "hordes of Hiver creatures" for scientific purposes set off a reaction that proved just how strong the militant annihilationists were.