As you probably know, when saving a map with these NPCs in it, the NPCs will duplicate an unkillable uninteravtice version of the NPC you spawned. The author is either unable or unwilling to fix this, and I'm pretty sure it's the first one. Regardless, after much pricking around, I learned that going to "user" in the spawnmenu and cleaning up NPCs after reloading yiour save only deletes the duplicate versions that you can't interact with. Hope this works for all of you.