It's a complex organism. As shown in the manga, its surface is entirely organic. A super organism on par with the Tyranids given how quickly it was able to consume and assimilate the humans that set foot on it. But still organic. Virus bombs would break that organic tissue into a flammable sludge, then hit it with torpedoes to ignite said sludge turning Remina into a blazing star for about a day before every trace or organic is scorched away.
Then the Mechanicus will use that planet teleportation technology they got from the War of the Beast that they totally shouldn't have but still have anyway because fuck you, and send the lifeless corpse somewhere remote where it can be studied at the leisure of the Biologis.
Unless the Inquisition is in charge of the operation, in which case, they'll teleport it out of the galaxy or into a black hole or something regardless how much the tech priests screech their binary at them.