For Vader dying, I've heard a few theories;
1. The lightning from the Emperor struck the exposed circuits in Vader's severed hand and this destroyed his suit.
2. When Vader chucks the Emperor down the chute, this blue energy is thrown back up and engulfs Vader. This was radiation from the reactor and this killed him.
3. Vader was "the chosen one" and it was his destiny to destroy the Sith. He was brought into existence by the force, a miracle birth, for this purpose. Once it was complete, he simply was taken back to the force, his job complete.
4. After Obi-Wan dices Anakin and leaves him to burn, the Emperor shows up and lays a hand on Anakins' forehead. This was actually Palpatine using the powers he described earlier to use the force to keep him from dying. When Anakin killed the Emperor, he cut off the source of this power and began to slowly die.
I kinda have a preference to the last one, as it fits in with the powers Palpatine was talking about in episode 3. Option 3 also has a nice, mystic element to it, like Jesus returning to heaven after his work was done.
As for episodes 7, 8 and 9, George Lucas cleared up this fan rumour quite some years back. Apparently, he was once asked in an interview, shortly after Return of the Jedi was released, if he intended to make another Star Wars trilogy sometime in the future and he said yes. He was then asked if he intened to go back and make episodes 1, 2 and 3 and, again, he said yes. It was assumed he was referring to two deifferent trilogies when answering these two different questions, but in fact, he was only ever referrring to the prequels.
I have to say that I would not want them to make a 7, 8 and 9. Not because I'd be worried that they'd be rubbish, but because episode 6 was a perfect end to the story. It still makes me sad to this day, watching the end of RotJ and knowing that Star Wars enRAB here and there is going to be no more, but that's exactly why there should be no more. It's a great end to a great story.