Danny Phantom Theories

If a Ghost loses the object of its obsession there are 2 possible things that are most likely to happen:

The Ghost in question will fade away

It will go rogue, becoming completely, & totally malevolent, destroying everything & anything it comes across (i.e. Dark Dan Phantom)

c) Will find a new obsession or become a "vegetable"(basically highly passive or in a coma-like state.)

Although the last entry is just a theory, there IS evidence that it should happen to a halfa, were it to lose its obsession. Because they're still human (somewhat) it's easier for them to adapt, much more so than ghosts

You see, the mentality of a ghost can be both highly complex but at the same time, also surprisingly simple, it all depends on how the ghost died. Not only does it depend on the manner of death, but also what the being was in life. Ghosts need an obsession to stabilize their form; otherwise they'll melt (1) or fade away.

Some full ghosts have been known to find a new obsession, although they are few. Let me explain, only if a ghosts' obsession is destroyed, but not completely, will they find something more substantial (usually closely related to their past obsession) to obsess over, stabilizing their form.

(1) Like Dani was melting in both episodes, Kindred Spirits & D-Stabilized. It wasn't the Ecto-Dejecto that fully stabilized Dani; all that did was give her enough time to find an obsession and grip on to it for dear life, both figuratively and literally. For Dani's stabilization 3 things needed to happen.

1. She needed to find an obsession.

2. Something to temporarily stabilize her form.

3. She needed to Die.