well they'll argue it's your fault because of the remote start but if they had the ebrake on it just would have stalled, maybe jumped a curb, but wouldn't have ghost ridden off into a pond
bottom line it was in their possession, they were operating it, it's on their property, and they left it with the ebrake off so it's their fault.
that car is done, you can't fix that but that's why you, and the dealer, have insurance. they totaled your car so their insurance will cover your claim. don't worry about the deductible, since you're not at fault the other insurance company has to cover it. the fight will be covering all your mods and paying you enough to get a new car. ideally what needs to happen is you get a new car along with the extra money to mod it the same way your old car was, that's when lawyers might have to get involved.
personally if the dealer is putting up any resistance don't even bother dealing with them, just work with your insurance company, they already have lawyers and that's what they do. I'd get to know why insurance rep real well and you'll have to be a squeaky wheel or they'll drag their feet. and remember you don't have to agree to everything, they can't force you to settle, drag it out for months if you have to. I had a claim when my first car was stolen, I dragged that out for 6 months till I got the money I wanted for it. sucks but don't let them push you around.