Just how many games do you think a manager is worth in a year? Because it isn't much, or they'd be paid a lot more ....
I agree with Seth, there is a need by humans to assign blame, when sometimes stuff just happens. This idea that he gets zero credit for the good years is ridiculous. His job either matters, or it doesn't.
All that said, the coaches and front office need to show that this year was the fluke, or there should be consequences.