I believe it is generally accepted on here that "As Aaron Rodgers goes, so go the Packers". The extension of this belief is that if AR went down for the season or an extended period of time (10 or more games, say), the Packers could effectively forfeit the rest of the season, because without AR, they wouldn't be competitive. Some examples of other teams who have faced the loss of a starting QB might be the start of some discussion. So, here we go.
Tom Brady had a season ending knee injury in (I believe) the first game of the season a few years ago. In came his unknown backup, Matt Cassell. The Pats could have been expected to really stink with the loss of their franchise QB. Instead, they had a very respectable season. Who woulda thunk it?
Brady himself replaced the Pats franchise QB Drew Bledsoe when Bledsoe was injured for a few games. They did OK, and the next year, NE traded Bledsoe to Buffalo (a division rival!) and made Brady the starting QB. A move that looked very stupid turned out to be incredibly shrewd. Who would thunk it?
In '99, Trent Green was the starting QB for the St. Louis Rams, who were considered to be serious SB contenders that year. Green was lost for the year in an exhibition game. His replacement, the then unknown Kurt Warner, stepped in. The result: "The Greatest Show on Turf"; two SB appearances in two years, with one victory and one loss. Who would thunk it?
Earlier, back in '92, Don Majowski was the Packers adored QB, the "Majik Man". He went down with an injury early in the season, and on came the unknown Brett Favre, recently gotten from the Falcons. The result: the Packers became a relevant and rising team for years. Who would thunk it?
Last year, Alex Smith was the steady game managing QB of the 49ers. The team had made the NFC championship game the previous season, and seemed poised for another SB run. Then Smith gets hurt, and in comes the unknown Colin Kaepernick. The 49ers quickly made him the starting QB, and were literally yards away from a SB win. Who woulda thunk it?
So, the question is obvious. If Rodgers were to be unavailable for most of the season, and Graham Harrell were pressed into service, would the Packers suddenly become a league laughing stock? Cellar dwellers for that season? Late night talk show punchlines? Personally, I'm not so sure. I think the team would rally around Harrell, and the Packers would have a respectable season, and quite possibly make the playoffs.
Though I really, really, really, really, really hope I never have to find out if this is true or not.