Yikes. That had to be quite an experience. I've seen many accidents, but never anything that severe.
My seat belt saved my ass about a month ago. Long story short, I was in my Lincoln Mark VIII, swerved to avoid a deer, skidded into a ditch, and hit a tree stump that was hidden under some brush.
I remember being slightly dazed, and annoyed that the car would not crank or show any other signs of life. I got out to survey the damage, and noticed that about a third of the front end and much of the undercarriage was missing in action.

The airbags did not go off, which was very surprising given the severity of the accident.
My sole "injury" was a scrape across my neck and chest from the seat belt doing its thing. The cop couldn't believe that I walked away without a scratch. If I didn't buckle up, I'd probably be facing reconstructive surgery right now--if I was lucky.
A few years ago, a friend of mine was driving on a snow-covered road. Some jackass passed him, and spun out into his path. He T-boned the car at about 45 mph. Because he was buckled up, he just got a scrape on his forehead from the sun visor.
Why people don't buckle up is beyond me.