How does that resolve him of the fault? Assume my explanation is the truth? After consulting with his attorneys he decided on a story that puts him in the car, trying to get back to the Edgartown Ferry. He takes a wrong turn and the car goes into the river. He dives countless times to save her and almost drowns himself.
In short, they paint the picture of the guy being a hero rather than the irresponsible drunk who left a single gal in his car, driving alone down a road to a dead end secluded beach etc etc.
The guy refuses to leave the Senate. Compare this with the countless others, including the clown from Minnesota who resigns over nothing, and people like Newt, and others. Kennedy stays in the Senate and does more to ruin our country then any one person ever. This includes the borking of Judge Bork and other cabinet choices that used to be the prerogative of the president to appoint.
Your theory is so drastically wrong that it’s probably impossible to convince you otherwise. Kennedy was in that car until it got to the bridge. Only he ever knew if he pushed it over or drove it over in a DUI accident. Either way, he killed Mary Jo. She was not driving. If she was, even drunk, she could have easily gotten out of the car on her own because the driver’s side was not damaged. Why you want to invent a theory totally at odds with all the facts is a mystery, but you do wind up clearing Kennedy of any wrongdoing except trying to unnecessarily make himself a hero while putting himself in the car. It’s screwy.