I know that losing Manuel is a huge blow to this team and the city, but whoever we sign will not be a massive letdown as everyone seems to expect.
First off, the Bills defense with Gilmore and Byrd(barring he is not traded) will play extremely well given our linebackers and front seven. Their secondary is their only weakness as far as I can tell.
Another thing, Buffalo's main reason they win games is their running offense and ability for Manuel to make short range throws/elusiveness. Bringing in a read option QB like Pat White will compare closely to what Buffalo now deploys.
Manuel's completion percentage would be similar to a veteran back up QB's percentage. White is not the best to throw deep but is enough to keep defenses honest.
Hackett does a nice job creating points and he will do the same with another QB.
Plus, the Bills' running game is actually what carries the offense with a few downfield throws when the defense stacks the box.
Second to last, this coaching staff has done a fine job coaching up apparent 2nd string talent to highlight their strengths and mask their weaknesses.
Finally, Whaly has done a superlative job finding good and proficient free market/waiver wire talent. I trust the back office to get a nice bridge QB. Him and his scouts have done a wonderful job finding players that fit our schemes well. I have faith in Whaley evaluating the right person to keep the offense moving.
The only thing that I will miss with EJ hurt is his continued progression and gelling with the receivers; plus his leadership.
In conclusion, I do not expect the Bills to be better or worse while Manuel is gone. I still believe Manuel is the face of the franchise for years (at least a decade) to come.