I'm aware of that,
Tropes Are Tools after all
I'm not claiming to be unique in a lot of respects. Likewise, I was giving some extreme examples, but in terms of writing I'm thinking some more subtle neurosis and a tendency towards egotism or indirectly suicidal tendencies, or tending to forgot (and as they get older, having trouble or being incapable of caring) that people are, you know, people and not just tools to be used and manipulated. The idea that eventually they won't even notice the line in the sand as they crossed it and won't be about to turn back or apologise, at least not with any sincerity.
My idea of Ghosts is effectively, well sure I'll explain ghosts here although they are an idea I am somewhat fighting with since I'm straying into Energy Can Do Anything! I'll probably leave this explanation as the "rough theory" being dolled out by someone only somewhat educated on the topic:
Ghosts) A person can either with knowledge or dumb luck, often when dying or being killed, create a kind of "construct" which is essentially an energy copy of themselves, their personality and traits. A ghost isn't the original person who died, they're simply gone, but a kind of 'imprint' of them left in the world. This imprint can have varying levels of sentience, being anything from creatures of anger and hate to effectively that person but in a less material form. They would essentially exist as a series of interactions between energies created in a specific way so as to manifest as if they were the original person.
However, as time goes on that energy slowly disperses into the surrounding world, causing the ghost to decay. Actually influencing the surrounding world requires them to expend some energy too, hastening the decay. Their powers and ability to influence the world weakens, and even the sanity of the ghost deteriorates into a much more base, primal personality. Eventually, they'll fade into nothingness.
Ghosts, especially the ghosts of wizards or warlocks created with preparation, can learn to take energy from the world and maintain themselves (Ghosts who can do this are what causes the "sensation of cold" reported on all those TV shows ^^).
Like I said, so far it's a topic I'm a bit vague on how I'll make it fit, it being a copy of the person in the "magical energies" mage-users work with seems the best I can come up with...