Captured Scenarios

What would've happened if...

X2 failed to save Luke from X1.

Vader never escaped after being captured by the Rebel Alliance after losing to Starkiller.

Different scenarios, explain how the aftermath of those situations would go down.

Vader deserved death, I don't think the Rebels would leave him alive.

I mean...
For Rebels to leave Vader alive would be like families of WTC attack victims allowing Osama Ibn Laden to live after getting their hands on him...

Starkiller would've grown more powerful to the point where he defeats Palpatine, would have been killed by Palpatine or would have been turned to the Darkside by Palpatine.