What do you do with a dead doomsday machine?

[The Lensman]

I'm in a mission in Star Trek Online where the Klingons have somehow gotten hold of the thing and are conducting experiments in order to use it as a WMD against the Feds.

 

[milo bloom]

Fill it with bean dip and have an epic party.

 

[Silvercrest]

Nail it to a perch and sell it.

Mr. Praline: I wish to complain about this Doomsday Machine, what I purchased not half an hour ago from this very boutique.

Owner : Oh yes, the, ah, the Norwegian Berserker... What's, ah... W-what's wrong with it?

Mr. Praline : I'll tell you what's wrong with it, my lad. It's dead, that's what's wrong with it.

 

[Kegg]

something which would sink to the center of the planet if it were made of actual neutronium.

A fair bit of Star Trek science only makes sense if they can treat gravity as something they can turn off and on and into a banana if they so choose; this is one of those things.