OUCH.
I would recommend something similar to AZIROC suggested, although I might personally first disclosed that "it has come to my attention that your car was involved in an accident while in their possession", without yet disclosing to them you got actual footage of it. I'm hoping this would bypass the inevitable and initial denial of the facts, and go straight to step 2
If damages are as bad as you stated, then I personally would push for a buy-back of the car and a like replacement at their cost. I know most will state this is unreasonable, and it may be... but keep in mind that a recent incident involving a C8 at Fremont Chevrolet here in the SF Bay Area being driven at 100mph+ in crowded streets being plastered all over the internet resulted in the dealership doing just that for the customer.
That's a bit of a nuclear option though... But I'd keep that in my back pocket if they're not playing straight.
Good luck!
Geoff