Is there a rule concerning the offloading of a missing passenger's baggage?
This question was covered over on travel.stackexchange and seems like there is a European reg on it.  


  In Europe, the question is covered by Regulation EC 300/2008. Annex I,
  section 5.3 reads
  
  Baggage reconciliation
  
  
    Each item of hold baggage shall be identified as accompanied or
    unaccompanied. Unaccompanied hold baggage shall not be transported,
    unless that baggage has been either separated due to factors beyond
    the passenger’s control or subjected to appropriate security controls.
  


I cant find any hard regulations but there seems to be some discussions floating around that would imply a domestic US flight may depart with your bags and without you here in the states. 

I can speak from experience while on a flight departing CDG for DUB the plane was held to remove a bag that belonged to a passenger that decided to take a different flight.