I knew that just losing the internet connection should never completely bork a save file, especially considering the files are located on his local machine which did not power down or anything, so it should have been able to save itself fine. I was aware of this but I had no other knowledge of anything abnormal that could be causing the issue. I knew the world would be far more useful than my assumptions so it all worked out regardless. As long as the machine doesn't crash during a write, as you stated, it should be fine. That is why I submitted the world in the first place, since I never would have been able to figure out the problem on my own and honestly had no idea what was up with it.
I actually understand now the process that happened, I believe. We were playing whatever the last version was when his internet crashed. When we got together again to play, we were several updates out of date. He updated his game and then, lo and behold, we suddenly can't connect to the server and it sits on the "connecting" phase. So, now we all understand what actually happened. Of course it makes sense now that I actually stopped to think about it.
