My experience is different from that of Hikertrash. My '05 (with original Zega bags, not the Zega pro) was dropped in the dirt, often. Typical damage was to the top where the strap loops bent. Blame that on the the camping gear. Real damage was always done on asphalt. Even then a 40 MPH low side did little more than grind away the portion of a corner. The almost high-side when I couldn't quite recover after losing the rear end due to some stupidity bent up one of the bags a bit. A medium size hammer on one side of the damage against a larger hammer (used as an anvil) on the other side of the damage was usually all it took to get things back in working order. And looking decent, too.
After that almost high side event the top lip was bent so I used a hydraulic jack to get it back in shape. I brazed up the bottom where it caught on some very rough pavement. All that was done at home. I never had the bags not get me home. That is durable enough.
I'm hoping for equal durability with the Nomada cases on the GSW.