Why would the Vikings pull their starters unless they were getting crushed by the Bears (it is not impossible, but do you see the Bears being able to crush any team with how they are playing)?
You DO know that the Vikings still have something to play for, with the 2nd seed all the way to the 3rd seed on the line. The Vikings have the same record as the 49ers and a Vikings win and a 49er lose assures the Vikings are ranked 2nd in the NFC.
The Vikings do not even have the excuse that the 49ers will have locked up the 2nd seed before the Vikings play, seeing that the Vikings play 3 and half hours before the 49er game starts.