Against Navy, he would have been a much better blocker than what was shown. I still remember the Navy pass rusher leaping over Armando Allen, then a true freshman, and sacking Evan Sharpley to seal the game. Darius Walker would have made that block, and not tipped his hand early during that play. The game wouldn't have gone into overtime with Walker in the backfield, for certain.
Purdue would have been much closer, maybe even winnable, with Darius Walker in there. There were many opportunities to get some passing rhythm going in the first half, but terrible blocking by the running backs caused Jimmy Clausen to get hammered pretty badly. Also, the running backs weren't running the pass routes very well either.
Other than that, I'm not sure that any other games would have been winnable.
To have finished 5-7 would have been a hell of a lot better than 3-9. It might have even given Charlie Weis another mulligan.