So, after consulting with Markham and Gargan, Teddy ran the car off the Dyke Bridge and concocted the story about missing the turn in the dark, hours of disorientation, etc. Not very good, but the best that could be done on short notice. The point being, they all thought MJK was dead anyway, so they were just avoiding a legal complication by keeping Teddy away from the breathalyzer until his BAC returned to a legal level.
As it turned out, she wasn't dead, and if Teddy and company hadn't been so concerned about political office and damage control, the whole thing could have been cleared up that night, once MJK came around.
He wouldn't even have had to wear a neck brace.
The story did not die with Kennedy. There are others involved who know what happened. Why they won’t step forward and be honest is beyond me.