a moot point

Check out the slow motion video at Cheesehead TV.
Ryan Pickett shoves the center into the path of the pulling right guard, which allows A.J. Hawk to beat the guard to the hole, and forces McGahee to bounce outside. Woodson never lets him get there.
But if Woodson misses that tackle, Collins has already shed the block of the fullback and is in good position to make a tackle himself. Which he probably would have.
If he didn't, B.J. Raji, who had previously engaged two offensive lineman on his own, and Brad Jones, who had crawled under the right end on the far side of the play, were both closing on the ballcarrier. Clay Matthews looked like he was held, otherwise he might have been in pursuit, too. Barring some kind of Keystone Kops routine, I don't see anything better for McGahee than sneaking out of bounds at the two or three yard line.
But Charles Woodson is a god. He made the tackle. The point is sort of moot.