I myself wonder wether or not Vader can use Lightning. He can use the Force on his hands, as we see in TESB where he stopped the laserblasts from Han.
So, to me, that means that he can still use the Force with his hands, them being bionical or not.
Yoda said:"The Force is everywhere."
But ever since TPM, there is this belief that "The Force is only there in your own body". I'm not convinced that is true.
The thing is, we don't see Vader do much Force-things. He chokes a few people, he walked to that broken window in Cloud City that sucked Luke out.
Beyond that, in the movies, nothing. I consider wielding a lightsabre not part of using the Force. Perhaps being able to foresee your opponent's moves.
The fact Vader could repel the shots from Han indicates that his hands can withstand high intensity rays, I think.
Also, what is Sith Lightning? I think it starts at the tip of your fingers, and isn't generated inside your arms, because then too, Sidious would buy it using it, as would any Sith.
Further, I think Vader died not from the Lightning bombardment alone, but he was exhausted as well.
Once Luke cut his hand, we hear Vader breathing very, very difficult. He has lots of trouble getting to his feet, and kind of staggers over to the Emperor. When he gets next to him, you can see him panting, his whole body is convulsing while trying to get the air in.
Lifting the Emperor, getting the hail of lightning, might have wrecked his body beyond recovery.
But, contrary to popular belief, his breathing aparatus still works, you can hear it.
As Luke lifts Vader's back up, you can hear that the breathing gets more comfortable, returning to alsmost normal.
Then, cut to the shuttle bay.
Vader is walking, assisted by Luke, and then simply breaks down to his feet out of sheer exhaustion. If his bionical gear would've been so damaged, including his artificial lungs, Vader would never have made it that far. Remember, the Emperor's throne room is in that tower we see Tie-Interceptors fly past. The hangar bays are in either the equatorial trench, or the 2 others north and south of that.
Even the shortest route is still quite a distance.
Vader made it to "a" hangar, not necessarily the same he arrived in at the start of ROTJ, but still, he went a long way.
All that combined, the pain from the lightning, being exhausted by the duel and the long walk to the hangar, that I belief is what killed Vader.
So, we now have to wonder why Anakin didn't die after getting his limbs cut and falling into a volcano and resting next to a lava-stream, causing him to almost fully burst into flames.