Which failed first--the inverter pump or the 12v battery?

I know that there have been discussion threads about the need to replace the 12v battery and the hybrid system inverter pump at the same time, but I’d like to run my situation by your expert minds and get your opinion.

My husband and I were driving my 2005 Prius with 75,000 miles at night along the interstate highway when a beep sounded, the check engine light appeared on the dashboard, and the “red car†icon popped up on the MFD. The manual indicates that the “red car†icon indicates a problem with the hybrid system needing immediate attention. We pulled onto the shoulder and called AAA.
We had to wait for nearly two hours before the wrecker arrived. Even though we were concerned about the battery we left the flasher and the headlights on for safety purposes. Shortly before we were rescued the power died completely—no lights, windows, or locks, etc.
The car was towed to a large Toyota dealership 30 miles from our home, and we left the above description of the problem and the keys in the night security box.

The next morning I got a call from the service rep that they had checked out the car and the only thing that was wrong was that the 12v battery needed to be replaced. I got a ride into town, picked up the car, and started home. After 20 miles the same lights came up again so I took it back to the dealer.

After another 45 minutes the rep came out and said that now the inverter pump had failed. When I asked why they hadn’t picked it up in the morning’s diagnostics, he said that in the morning when they did the computer diagnostics, the pump was fine. I told him that I had only seen those icons twice in the 5 yr., 75,000 mile history of my car, and both times were in the past 18 hours and 20 miles. I didn’t think it was a coincidence, especially since one of the icons indicated a problem in the hybrid system and the 12v battery was not a part of that motor. He said, hey, anything’s possible!

Here’s my best guess as to what happened. I think the mechanics saw that there was no power and replaced the battery before they did any computer diagnostics. Once the battery was replaced, the error codes were cleared from the car’s computer. So if they even did do a computer diagnostic at that point the earlier warning about the inverter pump would not show up. As soon as the car got out on the road again it reminded me that I had not taken car of the initial problem.

Obviously, I needed to get the new inverter pump. By keeping the lights on we were probably the cause of the battery failure. So I needed to replace both. But I’m just annoyed that I had to spend two trips, many miles, and lots of hours on this. Add to that the possibility that the guy lied to me, and I’m thinking that I need to find a new place for service.

If you’ve read this far, thank you for your patience. What do you think? Is this guy’s story believable or do you think that I have a good idea of what went on?
Thanks.