Update:
- I spoke with the dealer and asked about a partial repair of the wiring, i.e. replacing the caps. He said Toyota does not allow that as there may be unseen damage to the wires. Also, the corrosion seen will lead to wire damage.
- He was certain the car would be fixed after this repair.
- I spoke with the body shop. They said they have no idea if they had to open the tail light to replace the bumper. There is no note that it was done, but he said he can't say with 100% certainty that it was not done.

So, it looks like I am paying $1700 to get my car back with no one to blame. Toyota will claim it is the body shops fault. He will deny it. Sounds excellent.