Re: How to break up a circuit with a shared neutral?
One more clarification I don't know if I saw addressed was your question as to whether losing the neutral to the house is the same thing. It would be except for one fundamental difference. Your house main panel is tied to earth ground (water pipe/ground rod(s)), so although the incoming might be floating a bit if it loses neutral, it's probably balanced enough and tied to ground somewhere back up the line (at the pole transformer) so that the two hot legs are not straying to far. So even if your two sides in your house are not totally balanced, they both return to earth ground and you would not see the same kind of failures you might on the inside of a house losing a neutral with a shared neutral ckt tied to opposite phases. That's also why you don't hear too much about that kind of fault in the news. In fact, I'm sure power companies run into tree limbs breaking just the neutral wire all the time... with no damage to the house contents.
One other interesting item - from my brother. He once ran into a trailer which was NOT tied to ground. Lost neutral from the pole. When they arrived they found a pile outside of air conditioners, electronics, lights, appliances, etc. all fried from seeing 240v [or nearly]. Bonding the trailer to the neutral was ok, but maybe the owner should have then tied the trailer [or better, the main box itself] to some ground rods... ya think?