Why, oh why, is PvP combat so often and easily fought to the death?
Getting a little inspiration from the arcade classic Mortal Kombat, we can see that fighters do not die so easily. Only when one fighter deals the finishing blow is the other fighter killed (otherwise, he/she just falls down in exhaustion).
I propose something similar for Planeshift. Because killing is illegal, or frowned upon in PS, many may not want to engage in the act (due to the negative side effects, perhaps?). Instead they can enjoy fighting to a non-permanent, non-lethal end.
However, just like Mortal Kombat, a fighter in PS can elect to implement a finishing blow (if he/she is bent on killing the other). Many statistics can be factored into the equation that governs the success of the killing strike (such as stealth, whether a player is conscience, etc.). A killing strike can be attempted at any time, but there is a high chance of failing and being killed yourself. A failed lethal strike leaves a player open to be killed for free in self defense.
Any potential reward gained from the PK is balanced by the high risk of losing your own life.