It looks like it's missing the 'Drivers Box'
This is a set of 8 verts, in the c_Body mesh, that are painted magenta (255, 0, 255, 255) and they should define the corners of the cabin volume. (bottom left/right of the foot well, top left/right of the windshield, top left/right and bottom left/right of the rear cabin bulkhead)
The game should take these verts and construct a box in which it will try and keep the driver by squeezing and pulling where nececcary (if the box gets too small, driver gets gibbed)
You will also need to add the following line (or at least make sure its there) to the CDATA section of c_Body in the structure file
CDamageParameters:Add_DriverBoxVertexColour( 255, 0, 255, 255 )