if you have a solid state drive it will help. I switch back and forth between panniers and a backpack. I use a solid state drive for my work and another for my school laptops. I work full time and still go to school. I fell once at very slow speed (while clipped in). I ended up slamming my backpack into the ground. The only damage was the corner of the metal laptop exterior had some scratches.

I've also fallen with a laptop in my panniers. It was winter when I fell. I got into the habit of wrapping or surrounding my laptop with clothes. This time the laptop fared much better. I have yet to have a pannier fall off and bounce along the road though.