Possible, but if he hired Long and had significantly more success, enough to save his job. I would say it would be unlikely that they would have fired Sanford and hired the assistant. That rarely happens, if at all. When a head coach is fired, in any sport, due to lack of wins, an assistant is never hired. Goes back to the Rice's assistant hired argument. They could be extremely qualified, but its never done.
History has shown that coach Long is a significantly better coach, and I think that the football program would be in tons better shape now if they hired Long, then fired Sanford. But its a hard move to make.