I'm presuming that the anchor is anchored very well. (sorry

) Maybe welded to the driveshaft or something.
So to disrupt the ward you either have to.
A. Cause the driveshaft to deform enough to break free whatever is on it or move far enough relative to the body to disrupt the ward
B. Twist the body enough that it isn't really a "box" shape anymore or is significantly altered in relation to the driveshaft(such as if the roof were compacted).
In a T-bone crash the only way to cause those kind of alterations is to do something that would definitly put a vehicle into the "destroyed" catagory.
About the only ways I see the ward being destroyed but the vehicle only haveing a little damage would be if an attack somehow hit and destoryed/dislodged the anchor itself, or if the van went under something it didn't have the clearance for at high speed and the top got ripped of.