There were three player personnel situations that were known (or should have been known) early during OTAs or training camp that were not handled well. If these player personnel situations had been dealt with at the time, then it is probable that the Packers would have been able to survive the Rodgers' injury with at least a better chance of a couple of victories during his absence. These situations are backup QB, backup interior OL, and safety.
The signing of Seneca Wallace was not a problem, except that it came much too late. Graham Harrell was beginning in his fourth year with the Packers. The coaching staff should have known better what they had in him and brought in a veteran or even a young QB at the beginning of OTAs to compete with Harrell and Coleman for the backup position. If the Packers had had adequate backup QB play during these past 5 games, they could have won at least a couple of them.
At offensive line the Packers did have Greg Van Roten and Lane Taylor (on the practice squad to begin the year) as interior line depth. The problem as I see it here is that neither of these players appear to be seen as future starters in Green Bay; and both seem to be inadequte backups. Tretter was injured in OTAs, so his status was known early, and Van Roten went to IR after 3 games. Therefore, whether during training camp or after 3 games, the Packers had opportunity to find a veteran who could backup at both center and guard. It has been obvious that the coaches don't trust Taylor in this position, and injuries to Evan Dietrich-Smith have caused major reshuffling of the right side of the offensive line.
At some point during training camp it must have become obvious that neither M.D. Jennings, nor Jerron McMillian were progressing into truly NFL-caliber starting safeties. This would have been especially true when McMillian was unable to beat Jennings out of the starting job, not due to Jennings massive improvement, but due to the lack of McMillian's. There have been a few veteran FA safeties available, who though not world-beaters, may have been counted upon to make fewer mental errors and given up fewer big plays.
I will offer two possible explanations for why these moves were not made. First, under Ted Thompson the Packers have developed a draft (or UDFA) and develop strategy as the first principle for developing a quality football team. This strategy requires some patience with younger players to keep them around to see if they develop as expected. It can be both a strength and a weakness. In the case of Graham Harrell, it became an obvious weakness as too much patience was exercised and he was kept around too long and never developed into an NFL QB. Second, the Packers have lost several key personnel people to Seattle, Kansas City and Oakland over the last several years. These losses must have hurt the Packers' ability to scout and evaluate players to the same effectiveness as had been done in previous years.