What if Anakin killed Obi Wan on Mustafar?
http://www.theforcebook.com/article/What-if-Vader-became-Emperor
Just check out that article and read it.
I'm not sure if the pre suit ROTS Vader would have kept the death star in his empire or not, due to his dislike of the death star in ANH. But here's what I do know.
Anakin/Vader, as early as ROTS, was planning on killing Palpatine and taking over the galaxy for himself. He wanted to rule the galaxy in a dictatorship with his family, Padme in ROTS, and Luke in TESB
Palpatine was already on his way to rescue Vader because he sensed through the force that he was in danger. Just like in the ROTS video game alternate ending, if Anakin killed Obi Wan, the Emperor would arrive to greet a non burned, normal human looking Vader.
I don't think Anakin would have killed Palpatine right away, as he did in the ROTS alternate ending. He would have kept him alive with the power to save Padme.
Palpatine didn't learn Plageuis's power for immortality, so it's very possible that it was just a scam and that he'd let Padme die anyways, as that was just to bait/lure Anakin into the darkside.
In the plageuis novel there was a wierd midichlorian science experiment for saving people.
I think Padme would have died from a broken heart with an evil Anakin anyways.
I think he would have taken baby Luke and Leia and he would have killed the Emperor at a certain point later on, and he would forced luke and leia to fight to the death so that only one of them could live to be his new sith apprentice.
Just type in Emperor Vader in google. It shows the old middle aged OT Vader, but never burnt, and the Galactic Emperor..
Imagine the Hayden Version of Vader blowing up alderaan in ANH with the death star!
Vader killing Kenobi and becoming Emperor Vader in ROTS would have been worser off for the galaxy in the long run, with his kids being brainwashed and not being able to redeem him.
Awesome drawings of Darth Vader had he never been burnt on Mustafar.