"No, it's not like Excalibur," Killian reassured. It wouldn't kill him, not in the way Excalibur would - but he was tethered to that sword. His very soul was - in fact, whomever had the sword could control him, a puppet on strings, and all they had to do was whisper a command. Anything at all.
Of course, the only one who knew of the swords existence at all was Stanley - and he wouldn't use it to take away Killian's free will. Last the Captain checked, that wasn't something you did to someone you were in a relationship with.
Still, the fact that the other sword wouldn't kill him didn't mean Killian was eager to have a blade plunged into him. "Best case, it hurts a lot and dissolves the curse. Worst case, it hurts a lot and does nothing," he said, arctic eyes cast down to watch the glimmer of the light off all these Christmas ornaments. "But then I'd go back to being magic-free."
And it admittedly made life a little easier - he hadn't figured out if the price of power was worth his soul or not. Sometimes he was glad to be rid of that pesky soul anyway, and this Darkness could go on and blacken his heart, to hell with it. Other times - he knew he wasn't made to have this magic. Wasn't meant to.