It is a coin toss on what could happen when CARNAGE finds out she is missing. The demon god might choose to investigate further when it finds out that she can't be reached or overlook her absence because it isn't so strange that no one can reach her. She might be invading a plane and she doesn't want anyone to know so she kept her whereabouts secret. But if the demon god investigates and actually discovers the Reaper, then his days will end.
The Reaper's smile widened despite her threat.
That wasn't the reaction she wanted. So she made sure to drive the point home. "Every demon god will hunt you once they know what you are. You will have nowhere to hide. You have to release me now or CARNAGE will look for me."