The answer really depends on Montel's health. If he is 100%, I do think he can make a difference. While Williams and Kimble have shown some upside, neither are a versatile as Harris and neither have Harris's ability to make consistent positive yards in traffic.
If he is not 100% and cannot cut or doesn't have 100% strength, Harris might not be any more effective than our other RBs.
I don't believe in giving up. I want BC to win and play hard for the remainder of the season. Spaz is the lost cause in my mind. But Montel is not. So what do you do? I would wait a week. We should beat UMass without him. If he is still pain free after two weeks of practice, then you play him for Wake. If he's not ok prior to Wake you shut him down for the year. He's earned the rehab time, plus the redshirt would give the apologists one more excuse for this year.