You can get the death star in the demo, just go to the spaceunitsupers.xml file, and let the death star be for the rebels, and whala, you have the death star, oh and you might as well reduce the cost of it too.(But i've not tried firing the death star, so i don't know if it works)

afaik there was some bugs with it, not being able to see/destroy it or it caused crashes.

The death star works in the galactic screen, havent tried it in tactical

It does work in the galactic screen, but it won't in the tactical screen, because there is no death star model in the model.meg file. BUT the death star does work when you use it after a battle by dragging it into the destroy planet slot, but it doesn't show the destruction sequence. The planet just turns into an asteroid field.