Sorry to hear you want to give up, here is a diagram showing the AC electrical stuff. Connector G20 could easily be disconnected and left off, it would be as you said just like an electrical outlet in your house--just put some tape over the end if anyone is worried about the little kids.
One other thing, almost too obvious, but there is a 50A fuse inline to the AC from the pack--surely they checked to see if the fuse was blown? It can be accessed for change with the car on a lift.
If the AC plug were to be disconnected and the car would run, then it would be a big selling point in your favor.
My guess is that there are capacitors within the AC inverter that have failed or are leaky. Not something a wrench mechanic could repair, but an electrical technician could easily replace. i'll try to find a used one and take it apart to trace a schematic.
i agree that it could be a battery pack issue and would be a warranty replacement. Surely they tried charging the pack with a Level 1 EVSE to see if it went to the full 16 bars on the fuel gauge? If not they should. If it charges up to full, then that is another selling point in your favor. If it doesn't charge up, then they owe you a new pack under warranty.