Status = Success
Over the weekend I installed the repaired in the car and assembled enough of the battery to do a test: IT WORKS!! The car now starts again as of last night. It took two start attempts because engine had sat still for so long, but on the 2nd push of the button it started.
Many thanks to the people who have contributed, especially
@Ivanciprian2004, who pinpointed the exact failing component where the 12V was being cut off. I would have spent a long time before I figured that one out, no doubt. His additional advice and insights, online and offline, were invaluable.
@OneWireAt1 also deserves special mention and credit for all his good advice online and offline.
We now have 3 people that have applied the same fix, and at least two that have started the car afterwards. There may be thousands more out there that didn't have a fix, and still cannot get spare modules from VW. So keep repairing, and let's keep the jetta hybrids rolling for another 10 years!!
Note to self: Don't forget that the orange plastic High Voltage System Interlock (HVSI) must not only be latched, but also pushed inward after latching. Forgetting that was a bit stupid, but then again one can forget some details in 3 months. :-).