Flying/jumping doesn't instantly kill momentum.

Could it theoretically help to avoid *some* crashes? Yes

But in most cases, it'll just trade a frontal crash for a crash against obstacles off/above the road... Which is way more dangerous for pedestrians, buildings, etc.

Driver assistance can in some cases brake before an obstacles. But we've also seen Teslas drive into obstacles. Regardless if it's going to be driver assistance or a human with too much confidence in their ability to avoid obstacles... I wouldn't want to be near a Roadster leaping off the asphalt