Adywan has already given this some thought, he proposed using the shell from ROTS as the third Death Star :
adywan said:How about using the skeleton Death Star from ROTS. That would be easy to add to any needed shots and , as Darth Richard said, it would be destroyed with in the explosion as a ripple effect. Because its only in its basic construction, as sluggo said, it wouldn't need any plot changes as the rebels would still concentrate on destroying the almost completed version which is the main threat..
One thing that has always bugged me about ROTJ is that the imperial fleet was never completely destroyed, so did they just give up when the Death Star was destroyed? I'm going to be adding the remnants of the fleet being caught up in the energy wave and you'll see them being destroyed. I think it will give the destruction of the Empire more impact and will take this sequence away from the "ANH rehashed" feeling I've always had about ROTJ's ending. Another thing i always wanted to see that was in the script, and will be in my version, was when the rebels realise the shield is still up and some ships couldn't turn in time impacting into the shield.It could be fully complete or it could look like this painting of the first Death Star in a similar state of near completion to the second (which would give the Executor a nice bit of exposed under belly to ram into) :
But it could be fully complete or it could look like this painting of the first Death Star in a similar state of near completion to the second (which would give the Executor a nice bit of exposed under belly to ram into) :
