I don't think this is very fair. How can you die 'unjustly' in minecraft? Perhaps you didn't see that creeper coming. That's fair, those mobs were designed to creep up on you. Despite that, I've actually had to do this in the past because my sister played my hardcore world and got me killed. Besides that, I can't think of any way you could die 'unjustly'. I hope you all use this tool fairly, and don't brag to your friends that you defeated a hardcore world if you died.
There is actually an easier way to save your world. When you die in hardcore there are two options, one is to spectate the world and the other is to delete it. When you get to this screen click spectate. Once you are spectating go to "Open to LAN", click "Allow Cheats: ON", then type in "/gamemode 0". You will then be back in hardcore mode.