I'd like to point out that in today's press conference, Gene said that he knew Ryan Day was the guy weeks ago. Looking back, that could easily line up with the Maryland game, where Urban looked to be in considerable pain for most of the game while ESPN commentators droned on and on about health concerns.
My theory, should you choose to believe it, is that following the Maryland game, Urban approached Day about being co-HC for the rest of the season, with day calling most of the shots. This way, it would relieve Urban of the pressure he was feeling and would allow him to be more of a game manager. Not having as much pressure, Urban was more engaged and fired up on the sidelines ive seen since his Florida days. Under Ryan's guidance, the team played at a level not too far from earlier in the year when he was head coach. His performance against TTUN and Northwestern made the choice easy for Gene and Urban. It was written weeks before today.
It's even possible its been a co-hc situation all season, but im inclined to believe the Maryland game was what really sparked Urban to start seriously considering retirement.