Shem, I like your concept for the sequel since you are trying to get it out of a hard area in the star wars time line and bring it somewhere that allows for more freedom.
What I believe from the teaser is that He did die, but to play on the title force unleash is that his spirit can not rest. I'm assuming Yoda (since he knows how to contact force ghosts) that yoda could feel the disturbance in the Force and reach out to his spirit. Star killer will then go through a level before he returns to his body. He will then seek out Yoda through his vision of him..star killer will know where he is hiding. Yoda will become your new master but star killer is conflicted with hate and anger. Starkiller will continue his quest on his own...
I'm assuming that Juno dies and Starkiller will either blame himself or another. I don't know if she would die during the game due to your quest or that she dies just after you came back.
I do have to admit I have no idea where they are going to go with this but if they want to continue the saga of star killer they will have to do something like Shem mentioned at the end of the game since they can't kill him off again because they did that already in the first one.
I'm assuming the writers had the ending figured out first and build backwards the story.
I also think they will release the rest of the alternative star wars trilogy with DS star killer.
Just my 2 cents