I think that Josh Johnson will be a good backup to Cam. I'm sure that he can replace Joe Webb. I don't have a lot of faith in Joe Webb as a QB, although I think that he was brought in just to fill in while Cam is out. Josh Johnson was just cut by the Bengals.
http://www.bengals.com/news/article-1/Josh-Johnson-cut-Breaking-down-CFA-class/f942741c-687a-4a00-940e-5ff36bad76cb