I have had one major crash with "normal pedals", and one major one with clip-ins.

Both times I somersaulted over my bike and rolled on the tarseal road.

Both times the bike followed me and bounced off me before I continued rolling.

In that crash (with the clip-ins and doing about 30/32kph), my feet unclipped themselves...

I do not think there would be a big injury difference at speed.

I am not sure how that pans at lower speeds though, when the impact is less likely to remove your shoes from the bike...