It would be unsafe not to I can't wait to get one of those self driving trucks They have one legally on the road in Nevada. Chinatown you ever seen it?
If it were you under contract, in the trainer's truck, and the trainer was constantly texting, hitting the rumble strip, how would you handle it?
Called everyone I ever wronged and apologized , get all affairs in order , God , Buddha, Allah I love you all .... Just in case
If he truly thought the trainer was an accident waiting to happen, I don't think we (or anyone else) can hold him at fault for getting himself out of that truck. Easy for everyone to say he should have called for a new trainer but what if he was 3,000 miles away from the terminal in a box with another guy that's pi$$ed off at you cuz you ratted him out? Truck drivers have been killed for less. I might have done exactly what the OP did. If I were the company, I would offer him another trainer if he wanted. If he declined, then I certainly would not charge him for the poor training he apparently received.
Reminds me of a guy I teamed with once. Great man and hard worker but his driving made me very nervous. I never thought about ratting him out but another truck driver on the road called the company to complain about his driving. The next co-driver was better at driving but a complete nutcase/sociopath. Teaming? Never again!
Here's what you should do, contact a lawyer and talk to them about breach of contract, mainly putting your life at risk while training through violating state laws and regulations of the FMCSA - no texting, no distractions, etc. I would have him write the company telling them that it is their responsibility to ensure your safety and the safety of others on the road by making sure their drivers are held accountable and you are not going to pay a dime. IF they press the matter, then bring it to court with your video and see if the judge agrees with them, likely not. Did they fire this idiot?
I think this depends on what really happened. He hasn't answered (or I missed it) how much time elapsed? Did he give them an opportunity to give him a new trainer? Did he take reasonable steps to try to make things work?
This probably would get more input if it was in the Prime section - we are talking about Prime here, are we not?
A lawyer isn't going to do anything here except cost you more money. I am sorry you had a bad experience, but that's life. Litigation cannot solve all of the bumps you will encounter in life. Live, learn and move on. Pay what you owe or it will cause you more aggravation down the road.