Remember that by 2004, Favre was already 34/35 years old. Not many QBs play much longer than that, so I would imagine the Packers would have already started thinking about a replacement.
Hence I think Thompson would have drafted Rodgers if he fell to #24 irrespective of whether Favre waffled or not. Even Sherman had a look at JP Losman the year before but he went a place earlier I believe. Now, if the Packers had performed better in '04 (which is a different issue!), then the best player available might not have been a QB and Rodgers might not have been drafted. But I do believe a QB would have been drafted at some stage.
I'm sure the Packers would have been interested in drafting a QB they could develop. It's obvious that any QB sitting behind Favre would rarely get a chance to play, so the method of his maturation is already predetermined - sitting and learning behind Favre. Then, it's only a matter of drafting a guy and sitting him x amount of years till Favre calls it quits.
I think Sherman and Thompson would have pulled the trigger in any of the years 2004 - 2008 if the best player available was a QB.