See how the roof is racked sideways relative to the floor? That's the kind of thing I think of when I think about why chair rail is important. I suspect the wall might deform a lot more, or even shear off, if a similar crash occurred with chair rail weakened or removed.
And roof vent escape hatches. Those side escape windows probably won't open easily when the window frames are racked. I guess a person could climb out through the gaping windshield hole, however.