The emperor is not dead for multiple reasons, it is stated by the last bit of story with kira, and in emails from the hand as a sw. also bioware wouldn't kill off the main bad guy straight away.
he was the voice, so a portaion of his true power and they kept making him weaker and weaker by the time your jedi gets to him (I mean making the voice weaker by too much power in the ritual and just having being killed by sw).
in terms of exile being killed off like that, I do also agree it was annoying as I would of liked to see her in action a bit more as she had a whole game on her, as for revans power being par with our characters, I think we are far from him power wise. as he was not at the emporers level but he could stand there in his presence and not be courpted. he could fight him for a little while too (he was never going to beat him 1v1 which is how it should be as good characters are not over powered and it's the main bad guy so he should be stronger then everyone else.)
He will come back as an opps boss but not for a long time unless they can find another vilian of such power to fill in the gap. as for scourge not knowing about the voice and so on. we can only speculate. as no story has come from bioware. He wasn't there so I just assume that is why. and maybe the version of the emporer that turned jk evil for a time was him as he was a different character model compared to the end of jk.
This has nothing to do with the thread. He asked about Scourges vision. He knew the emperor was still alive.