Transmission fluid and alternator?

Thanks all! So, the car is ready, and the dealer mechanic says the car drives fine and the transmission does not appear damaged ( he said there would be pieces of metal in the fluid and transmission if there had been damage?). Since they think it drives okay I guess my best is to drive it myself and be more hyper aware than usual to changes in how it drives. Any advice on what to look for? Before there were no signs until the exact moment of failure…