Oh, I'm so sorry you were in an accident but so thankful no one was hurt. The reason your back bumper doesn't look bad from the outside is probably cuz' of the rebound springs they install in case you have a minor fender bender, they're designed to pop the plastic back out, but obviously it did some serious damage, might have even bent the frame (totallying the vehicle). Just know that if insurance fixed it and it doesn't drive the same, take it back and continue to complain until they total it and just give you money to buy a new one. Otherwise, it could turn into a bigger headache with all the little things that go wrong, tires wearing funny, car handles strange, just little stuff most people wouldn't even associate with an accident that happened before a vehicle was repaired.