It's possible. I've dropped mine since I've modded it, while not directly on its back, but still haven't had a problem. The SIM and all the other components are still hidden behind the plastic case.
I had the same question about the extended battery and the OtterBox case. I ended up modding the case and getting it to work fairly well. Just uploaded a video of the finalized case.
Samsung Galaxy S3 Extended Battery w/OtterBox - YouTube