Remember, when a Construct dies, the essence is preserved. It would merely share the information it had gathered once it reconnected to this universe again. Hence why the Ethereals are more inclined to perform and participate in suicide missions. And it couldn't take control of the ship, seeing as how there is no actual intelligence to Possess. It could try to Possess the command crew, but wouldn't know how to operate the ship. Seeing as how for most species, a ship or vehicle is a tool seperate from the being, rather than being one and the same.