Would the HV "neutral" shift with the unbalance and difference between this "neutral" and the rest of the power company "neutrals" in the area, result in current thru all available paths like the plumbing and the earth itself?
If you are talking about losing the neutral on the line side of the pole pigs, it would really depend on where you lived. Some places have a better "ground" than others. If this was metal water piping, all the way back to the pumping station, you might not even notice the neutral was gone. If you are in Florida with plastic piping and sand around the electrodes, you are still going to balance the loads and the neutral will track that ratio. This is where you could be saved by diversity. The more customers you have on the load side of the break, the better chance you have that the loads will balance. It is still going to be pretty unstable.