There was a collection of injuries that year too, including Matthews (you had a hurt Mulumba and Jones as your OLB after Neal got hurt in the playoffs too) EDS at center and Barclay at RT.
But probably the two most critical issues: 1) the backup QB was not good. Flynn got hot one half (Dallas) and 2) team spirit - when you lose a league MVP and know your QB sucks, it brings everyone down - see Colts, 2011 for example.
This is why it will be so critical for Hundley to play reasonably well, and APRH.