The D did NOT collapse. They did exactly what MM wanted them to do. He starts counting possessions anytime he has a certain lead and he changes the way we are playing the game. This has an adverse effect as it puts players into passive mode (sort of like not calling enough running plays does to an OLine.)
Once they are in that mindset they don't come out of it again (thus the easy scores for Seattle to take the lead and in OT).
He does it every game which is why we have to sweat onside kicks after having 20+ point leads so often (see Atl).
I don't mean to say I want MM fired, he is a fantastic coach. He has a weakness and its his desire to milk a clock instead of go for the throat. Players excel when playing downhill. IF...he learns from this, it will be awesome, but if next season we have first half blowouts, and then must cover onside kicks, or make defensive stops to win at the end all season long I would say he didn't learn a damn thing.
Edit: He did learn that you can't play well outdoors after practicing indoors all week, so there is hope.