^^ lol that is actually an interesting point and does say something about his abilities.
Darth Sion was a tortured soul and in his final moments he died... the only way he could die was to let go of the dark side that held his shattered body together. His final words implied he found peace with his death and this was enough to do this.
I'm sorry but Darth Sion is dead.
Originally Posted by jonathan7
After Obi-Wan had beaten Vader he kept himself alive due to the DS untill the Emporer found him.'
ONLY Darth Vader could have survived his. Remember, even though he never reached his potential due to these injuries (losing literally around 60% of you total body mass and recieving critical burns to your body and lungs) it was his emense powers that kept him alive. Remember that he was still one of the most powerful Sithlords ever, even after being maimed.
We don't know that Sion can regenerate limbs and i think it's pretty clear as day that he cannot. However, the loss of an arm or leg would not stop him as it would somebody else. A normal jedi/sith would drop their saber and fall... Sion would have the choice to continue (even though you may as well yield).
I think if the game makers made a cutscene of the final battle with Darth Sion it would have shown a series of duals, each with Sion ending up with a heavy blade mark across the torso. The would glow red for a moment (he would do his shakey thing he does when beaten) then it would just turn black, blending in with the rest of his scars.
just my opinion