I don't really understand why Maggie would be glued to Barnabas' side as a Josette clone once she became a vampire. I think that's wishful if not highly deluded thinking on his part. She could just turn into a bat and a fly away the second he wasnt looking, or she could get her own 'Willie' to kill Barnabas. Paradoxically, it seems that being locked into a hopeless, tedious existance in that coffin for so many years destroyed Barnabas' ability to think long-term.
I agree-- but what Barnabas is trying to do is so fundamentally insane that you have to expect all sorts of glaring flaws in his reasoning. Vampire stories have often had "slave" vampires though, haven't they? These would usually be the "brides", who are enslaved to the vampire who "made" them... DS's makers may not have made up their minds yet about whether they were going to use this idea.