Not Turning On After New Key

Hello everyone. I have quite the nightmare going on and I'm hoping you fine people might guide me in the proper direction. I have a 2010 Prius that had been acting up with the infamous P0A80 error code. I went and purchased a new traction battery to put in. That very same day, I lost my only key fob. After searching to no avail for a few days, I decided it was time to call a locksmith.
They came and did their magic with a lot of trouble along the way. The key said it was paired according to their diagnostic software, but wouldn't unlock the doors, and the ignition wouldn't turn over. They then disconnected and reconnected the 12v battery. After this, the car wouldn't turn on at all. No hud, no head unit, nothing. The man said he couldn't charge me in good conscience, left me the key, and asked me to reach out to him in a week if it works or not.
That is my story, kind Priusfolk. I have a few hypotheses:

1. The 12v battery just died from the car being on without the engine running for so long while he tried to re-key the car
2. Something with the hybrid system already being wonky set me up to fail from the beginning
3. The dude was clueless and really fucked something up bad in the ecu when he was in it.

I'm in a really bad spot here, guys, and would appreciate any input you may have. Thanks.

 

I have not done anything with the hybrid battery yet. The old one pulling the errors is still in the car. Nothing lights up when I push the go button now. From what I have read and what it looked like the tech did, you can make a new master key by wiping all the old keys from memory. I believe the fob is proper as it looks like a widely sold aftermarket one for my model.