The topic of Democritus' zombies is interesting, great sources for that! "Stories of people who appeared to have died and then came back to life were collected by many of the ancients including the scientist Democritus in his writings...
Bryan I have the feeling that there is more going on here than I understand. I would think that anyone of normal experience would know that there are "degrees" of sickness and disease, including being "knocked out" and in "comas" that would present interesting questions of how "far gone" a person is before death. That wouldn't seem to me to be so exotic as to pose a particularly difficult question, and I think we have instances in Lucretius where it is spoken of that the spirit retreats within the body.
I suppose everyone was interested in this just as to what it says about how life operates, but I don't necessarily see why the Epicureans would be critical of Democritus on this unless Democritus were trying to draw from this some conclusion about the soul to which the Epicureans objected.
Do we really know and understand Democritus' religious views? Just because he was an atomist, does that mean that he had rejected all supernatural influences, or did he perhaps try to integrate the supernatural with his atoms, perhaps due to some issue deriving from his determinism and skepticism?
I sure wish we had more info on Democritus!