I'm looking for a way to have someone cheat death by leaving their body on the material plane. It's still active and it has it's own personality with absolutely no changes, like a lich. However, their soul moves on and turns into an outsider like a normal passed-on person.
Originally, I was thinking about a construct that worked via using the person's original organs, such as muscles, brains, et cetera. Think like an alchemical golem, but far more advanced and sophisticated. That, or a clone of some sort.
The story is that somebody comes up with a genius way to keep tabs on both the material plane and one of the outer planes. His body "dies" and becomes the sentient construct while his soul moves on to whatever depraved place he deserves. The problem kicks in later when the soul comes back with completely different ideas in mind. The same person takes two wildly different paths, kicking off the story.
A body without a soul by definition is a major change. The soul is what makes a person unique and without it the person would change. Having your organs means absolutely nothing as far as personality goes, otherwise a person who received an organ transfer would become a different person. The only way this could work in any way would be to spit your soul, and look how well that worked in the Harry Potter series.
Androids do this in their life cycle. When the soul departs the body, the body rejuvenates over the course of time and a new soul enters. Now, if you want to preserve your memories, i.e. Copy yourself without a soul, a neurocam and a clone pod can do it (Technology Guide) as though through a simulacrum spell (loss of 2 charisma points, however). Downside is that your copy can't get more powerful. It is soulless and can't get more experience.