Celestial rust monster vs grave knight

[RealAlchemy]

In a theoretical half joking discussion after a game, we were talking about how to permanently destroy a grave knight. I suggested a rust monster with the celestial creature template to get rid of the armor. If not, could a half-celestial rust monster do it?

[Adjoint]

The Sixfold Trial, p. 85 wrote:

In death, the graveknight’s life force lingers on in its armor, not its corpse, in much the same way that a lich’s essence is bound within a phylactery. Unless every part of a graveknight’s armor is ruined along with its body, a graveknight can rejuvenate after it is destroyed. A typical suit of full plate graveknight armor has hardness 10 and 45 hit points, though armor with enhancements or made of special materials proves more difficult to destroy. Merely breaking a graveknight’s armor does not destroy it; it must be utterly annihilated, such as by being melted into slag, cast onto the Positive Energy Plane, or sunk into the crushing depths of the sea.

If being melted into slag counts as 'utter anihilation', then being eaten by a rust monster, even ordinary one, would count as such as well.

I'm nost sure though, if just destroying the armor would destroy the graveknight. By RAW, it only prevents him from regenerating after his body is destroyed, just like after destroying a lich's phylactery you may still have to destroy the lich himself.

[William Werminster]

I'm sure a certain lich inside a Bag of Holding filled with holly water would love to know that answer too.

[Goblin_Priest]

Normal rust monster seems sufficient to me.

[Torbyne]

Though as a fun plot hook you could then do something weird with the Rust Monster that ate a Grave Knight. Possessed maybe? Or some undead template on it? Moral of the story, be careful what you eat.

[Saldiven]

Torbyne wrote:

Though as a fun plot hook you could then do something weird with the Rust Monster that ate a Grave Knight. Possessed maybe? Or some undead template on it? Moral of the story, be careful what you eat.

Rust Monster with the Graveknight template?

His "armor" for rejuvenation would be a particularly evil poop he took soon after eating the original Graveknight.

A Graveknight Rustmonster would be the terror of all Paladins, everywhere.