He is a good coach. I would not want him as my head coach for sure. And I thought it was the right time to move on from him as defensive coordinator as well.
If I had a young team just starting out with a new regime and QB, etc., he would be an excellent candidate for defensive coordinator. But it sounds like he is not interested in a coordinator position anymore.
But I don't think "13 seconds" is a major decider for anyone but Bills fans. Yeah, it would be one thing that might be considered, along with other failures, and they would consider all of his successes as well. Nobody obsesses about "13 seconds" like that besides Bills fans. For everyone else, it was just an exciting moment in an exciting game and spoke more about Mahomes and the Chiefs.