Thank you for your post , it helped me to remember some facts about Vader..things that I think killed him.
Way I look at it now(even though at the same time I agree with my script reasons for his death) was that Vader was already dead. The only thing keeping him alive was 2 things life support and Dark energy(hatred). Suppose the emperor designed his suit to be only functional from dark energy so that when/if Vader lost this he would die ending the emperor's threat from the chosen one to remove HIS power(bring balance). This is exactly what happened (only not in the order the emperor wanted)....when Vader let go of his hate(after killing the last thing he truly hated more than Obi Won) there was nothing left to fuel him= death was next.