If you read the book of sorrow the only way for permanent death to be inflicted on oryx or his siblings is if they are killed in their "throne" Later in the book it will go on to explain that oryx made the dreadnaught his throne to provide himself with the potential for endless expansion so his worm could be maintained more easily Story in the book of sorrow is great, I'd reccomended giving it a read. I'm looking forward to facing off later against Xi-Ro