It's a tough call. On one hand, if Beck IS the #2 guy then he needs to be on the field in Taylor absense. It would be dumb to put Ganz out there just to save the redshirt. If Callahan put Ganz in, to me that would have put the message out there that NU wasn't interested in winning the game by intentionally not putting their best foot forward.
In the other hand, you have his true freshman redshirt. The coveted 5th year of eligibility. The probability that Beck will take a redshirt any other year but this one is infantesimal.
Tough call, tough situation. I would have tried to save the redshirt considering it is so far into the season. He helped win the game today, although with that INT he could have lost it as well. Hell, it couldn't have been any worse than Davis's outing at TTech last year.