6 years as a firefighter taught me that if you wear your seatbelt, it is very difficult to die in a car crash, even a relatively high speed one.
It also taught me that it is very easy to die if you are not wearing a seatbelt.
I can't tell you how many times I was first on scene to a 50+ mph crash, even head on or rollovers, and the cars were smashed to shit, but everyone in the cars was completely fine, not much more than some scratches or bruises.
In many cases, all occpants were out of the vehicles and walking around before we even got there.
But if anyone wasn't wearing their seatbelt, they were seriously fucked up or dead on arrival.