I would bet that the princess we see is real. And that very evil spirit is not for his protection, but to protect her. Basically magic shackles. Or magic Geass. I wouldn't be even surprised if next chapter that guy starts killing his own people, like Euphie.
In the end the Princess will return to Hyperion, since that was the deal with the mages.
I also wouldn't count on mages swooping in and saving her. Wolf Fur knows that she had magic restraining tool on her. And Princess was kidnapped from apparently high-grade magic barrier. Sudden appearance of 2 most powerful mages of Arcus would be too fishy with all these leads.
Now that they disappeared with the necklace and we know that kidnappers will be all killed (the spirit is a big hint on how it will happen), noone will have any proof of Arcus having a hand with this kidnapping.
The only question is how will Princess behave.
I bet that she will make it all happen in such a way, that she will be credited with solo'ing everyone. This will stop any more kidnappings and assassinations (I hope, they are getting tiring) since everyone will know that 3rd Star is a true monster/genius that can kill/neutralize everyone and everything in her way.