Got rear ended on Friday, 4 car accident. Need some advice

For context, I was on my way home from work coming up to normal rush hour traffic at highway speeds. While slowing down, a driver in a U-haul van wasn't paying attention and hit the car behind me very hard, most likely totaling that car. The car behind me then hit me, and I hit the car in front of me. I had no significant injuries other than some neck/back soreness and a minor concussion. I went to urgent care and this info was provided to my insurance.

I am financing a 2020 BMW M340i with 35,642 miles. KBB says the worth is $41,155-$45,028 private party. $37,413-$40,884 trade-in.

I still owe $28,287 on the car.

The damage to my car seems significant. At the very least, my front bumper, rear bumper, and rear tailgate will need to be replaced. Most likely the rear frame bumper will need to be replaced or repaired as I was hit pretty hard. The paint is Mineral White, an upgraded BMW paint. I'm assuming the rear quarter panels and front quarter panels will need to be painted to blend in the new panels.

I'm hoping the car is totaled to make the process easier for me, but in the event that it isn't (which seems likely? I'm unsure), I'm looking for advice on how to be out the least amount of money I can. If the car is repaired, I'll immediately be upside down on my loan. I'm also unsure of who's insurance will pay the damages, as the U-haul van will be at fault.

How can I come out of this holding the bag the least? I see people mentioning diminished value, is that something I can start through U-haul? Should I contact an attorney? I can provide more detail if needed. I'm pretty heartbroken about it as I loved this car so far and haven't even owned it for a year. The car is dropped off at an autobody shop, and no communication has been started with my insurance adjuster other than starting the claim. What should I do come Monday? Thanks for your help.