Risk/reward was bad . Nebraska had taken control of the game at that point, scoring 2 quick tds to start the second half. The failed onside gave northwestern some momentum and great field position. 5 plays later northwestern scored and was back in the game.. Nebraska never had the momentum back the rest of the game.
IMO it was an unwarranted risk. I would have been a bigger proponent if Nebraska was having trouble stopping Northwestern offense, but that was not the case at that point.