Pat, what made you reconsider what PN's are from your initial thinking?
PN's are not super nova remnants. They are as you said the nebulosity left after a star has shed its outer layers, leaving behind the star's core, now termed a white dwarf. But not condensing back to form the white dwarf.
The white dwarf is not a star in the normal sense that is converting hydrogen into helium - its fuel has been depleted which is what triggered the disastrous shedding of a major % of its mass. The white dwarf is really nothing more than a cinder that is glowing from the residual energy created/generated inside the core eons ago, and is slowly bleeding out this energy until it has no energy to release and is a dead, cold and dark mass.
It may or may not have any of its original planetary system left still orbiting the cold core - don't forget that the planetary nebula phase saw an enormous amount of the star's mass lost, in turn meaning its also lost a huge amount of its original gravitational power, so much of the original solar system may have been also lost as the core alone does not possess the gravitational pull to retain the solar system - planets, comets, asteroids, etc.
Makes you wonder what a spent, cold stellar core looks like?
On the matter of stellar evolution (& sorry, a digression from the topic as this thread as sparked a question not totally unrelated though), what's with the stars that form globular clusters? These clusters are very ancient, but the component stars seem to defy what we know as typical stellar evolution - these stars should have gone past their main sequence phase a LONG time ago, yet so few PNs are ever seen in GC's and yet these stars keep shining, larger than our Sun, much older than our Sun, but still not evolved beyond main sequence...
Alex.