Sorry to hear about your accident and good luck fighting with DJI. I had something like this happen to my P3P but got lucky and it didn't hit anything. I was scouting a property that was for sale and dropped down to get the phone number off the For Sale sign. The P3P went behind a metal storage container and I lost signal. The next thing I see on my screen is the ship heading for home, even though the return home altitude is set at 100M. It didn't climb to 100M, it just started heading for home. On the screen I see it just miss the top of the storage container and a mobile home as the signal came back. I pushed the stick up to gain some altitude and missed the top of a small hill by about two feet. In the end, all was well but why the bird responded like it did is a big fat mystery. After losing signal, it should have climbed to 100M and then headed home. It didn't do that, it just headed home. Now, if it would have hit something, would that have be my fault? The way DJI looks at it....YES!
If you set the failsafe RTH height to 100m, then shouldn't it show as such in the flight log? In the event of a RTH crash, if it should occur at lower than RTH elevation (with sufficient battery), the flight log should show the Phantom somehow malfunctioned and didn't do what it was programmed to do. I think you may have a good very case for claim.