Maybe this is a little Vader clone, like the Fett dad/son story line? Annie 2.0 clone plays dress up and runs around on the empires bidding, most as symbolism. Then gets his not as awesome as the real Vader ass handed to him when he encounters a true sith and their built-in desire to be the top dog.

Or maybe some rogue group uses the Vader persona and look in their cause (oh look, we have vader on our side, grovel!!!), and this chick who's a true sith of the empire said fuck that shit and ended their little charade and proceeded to annihilate this rag tag start up group.

That's the only way Vader would ever get his fucking head cut off, if it wasn't actually Vader's head inside the helmet!