Why the powers can't be taken back:
A common justification is that breaking free from Old Scratch's control is the very thing that
stops the Devil from taking the power back. The Devil could only give the powers in the first place if they gave him control over them. If he no longer has control, he can't do anything directly to that person besides sending in his
Mooks to try and kill them off. This may be best understood by way of an analogy: the villain is a computer and the hero is an MP3 player. As long as the MP3 player is plugged into the computer, the computer's user can add and delete music files on the MP3 player at will. But once the MP3 player is disconnected, its playlist is fixed, and it is free to
rebel against and ultimately destroy the computer.
Why else the powers can't be taken back:
If you lend someone your car for the afternoon and they unexpectedly take it on a road trip, what can you do about it besides reporting your car stolen? There's no reason to assume that the demon should have the ability to reclaim something they've given away. That's not how possession works in real life, and any systems in place to make it work like that are things we've created. And most of them involve having third parties try to get it back for you (the aforementioned Mooks).
