The thing is, the driver which caused this mayhem probably didn't intentionally flee from the scene. Something like this (on a smaller scale) happened around me a few months back, the driver was stone cold sober but he fled due to shock.
If you accidentally caused something to big, you'd be in shock, not knowing what to do you would probably flee too.
I know that drink driving is wrong, but maybe he didn't intentionally flee
Pretty sad for the family with the wrecked Mercedes, their not a cheap car.