Don't crash victims often go through the windshield when they aren't wearing seat belts? Will an airbag stop this even if not buckled?
Yes.
No.An airbarg is not/less effective if you're not wearing a seatbelt.
It's designed to keep your head/face from hitting the dashboard and windshield.
Without a seatbelt you will just fly above the airbag and hit the windshield.
You can still get a concussion (your head hitting the windshield) or break your neck, and die, even if you don't fully go thru the windshield.And even if you have airbags in your car.
The airbag alone won't keep you from getting ejected from the car (from either the side window or windshield) during a roll-over or a head-on collision.
This video shows the difference between sealbelt + airbag , and no sealbelt + airbag.
[video=youtube;9_Af8w2SAT4]https://www.youtube.com/watch?v=9_Af8w2SAT4[/video]