Unfortunately - accident in customer's cars is a somewhat common thing at most dealerships. As much as I'm sure you would prefer not to hear it - I'm predicting that the dealership will dig in deep and insist on repair to original spec. With an attorney you may reach an agreement on diminished residual value - but don't count on it. Also consider that you will be paying an attorney at a hefty fee to work on this - balance that with what you realistically expect to gain.
If you threaten to sue - count on the dealership to refer the matter to their attorneys (who get paid to do this over and over and over) who will stall and delay while your car gathers dust on some back lot while you continue to have to make payments on it and have to find a loaner. If you refuse (initially) to let them repair it - they will probably withdraw any loaner you may have (stating that you refuse to allow them to make reasonable repairs).
Note that they are experts at playing this game. You are possibly the 25th person this year whose car was damaged in one way or the other by service staff. They are used to it and threats will do little or nothing to concern them.
Wish it was a cheerier picture but this is how the game is played.
ETA: Don't expect ANY help from BMWNA.