I havent had the chance to read the entire thread, so forgive me if this has been addressed. But my idea for the reason Starkiller is still alive goes back to a fanfic I wrote after the first game came out.
When Vader impaled Starkiller in front of the Emperor, my fanfic story was that Vader actually cloned Starkiller. The cloned Starkiller went on to continue the game and die, while the real Starkiller was now changed and seeking revenge for those who betrayed him. Vader. My story had Starkiller as neither Sith nor Jedi, simply a force user who was pissed off with his master. He had no intention of becoming a Sith Lord and didnt want to fight against the dark side.
Anyway, that was something I wrote and an idea for how Starkiller could be in the next game.