In most places they refund the entire bet price, which includes the juice too, so really no one wins or loses in that case, at least in the category of pushes.
Now if you're talking about "middling" (and I think that maybe mgteich was), then that's a whole different ballgame. That's when the bookie falls in the middle of the line movement and ends up paying out too much action due to the score falling in the middle of the lines. I think that is why they are pretty careful not to accept too much action on one number, and that's why the odds (-110, -115, -120, etc) and pointspread change accordingly.
I believe that it happened in one of the two old PGH/DAL Superbowls in the '70s, but I am not specifically sure as to which one.
The bookies had a nickname for it, I think. IIRC, it may have been called "Black Sunday" or something like that. Now I think things are more carefully planned due to mistakes being learned and the technological advances.