Of course it depends on the situation. But when a lower level object or system communicate with an higher level system, should callbacks or events be preferred to keeping a pointer to the higher level object?
For example, if we are working on a game, we have a world class that has a member variable vector<monster> monsters. When the monster class is going to communicate with the world class, should I prefer using a callback function then or should I have a pointer to the world class inside the monster class?
It generally is preferrable to use callbacks to communicate with higher level classes for the reasons you mention and to avoid mutual/cyclic dependencies.
In your case, you still have to define what is the lower level module. Should world really need to know what a monster is? Aren't monster just creatures or opponenents? Doesn't monster need some kind of environment to act in? Only you can answer that to come to a workable solution.