he's going to lose for sure.
He had his foot on the guy's neck and at just that moment, he died for an unrelated reason?
No juror is going to buy that. It's such a poor defence.
He'll be much better off admitting he misjudged the situation, thought he was acting in the way he was trained to but now realises he got it wrong, saying the death was unintended and not done with malicious intent, apologising to the family and throwing himself on the mercy of the court.
Some of the jurors might believe that sort of explanation and make him guilty only of manslaughter.
But there's no way, seeing that video, they will buy the notion that he didn't kill the guy by standing on his neck. And they will hate Chauvin for thinking they are dumb enough to believe him.