I am heartened by the report of a Vancouver Prius 1 Taxicab was repurchased by Toyota and replaced by a 2G model. The taxicab had over 200K miles on it and worked perfectly. Toyota bought it back to study all of the things that went right. If a Prius 1 THS system can survive 200k miles in taxicab duty, I am quite confident that a 2G HSD will do better, especially the way I drive it.

I don't really know if HSD can run without the HV battery. But as someone earlier mentioned, since there are twenty-eight 7.2V modules, it's not likely that all will go bad at once. The Battery ECU would compensate by optimizing what is left of battery capacity. When battery voltage is no longer sustainable, I suspect that the Battery ECU would tell the Engine Control Module to keep the ICE running so it would function much like a normal car. I have no knowledge of what would actually happen but is seems that the engineers would have designed such a failsafe into the system.

I plan on finding out for sure, many years down the road. I think 300-500K is my target. On a related note, since I have successfully added battery capacity to my Prius, and have since removed said capacity, I know exactly what to do if my HV battery goes dead.

It's a Wonderful Day for Science!