The case coming off during a fall shouldn't be much of a problem. In fact, doing so would take away some of the energy of the impact. If you watch Indy car racing, their cars are designed to come apart easily just for this reason. The energy of an impact is taken away some by the pieces coming off the vehicle.
Of course... I have had problems with the case for other reasons. The thin strip on the top bezel near the volume button has now busted TWICE. Exact same place. Unfortunately, I can't get to a Sprint run Sprint store (the ones around here where I'm vacationing are owned by a third party), so I'm now outside of 30 days from my original purchase. They replaced the first which broke after 2 days. Not sure they'll do it again.