Dying in a Hardcore world and clicking Delete World causes the game to still think you are in the Hardcore world. You can see images of your death and still interact with the game on menus and loading screens. The world is also not deleted and can only be deleted manually (by going into the .minecraft folder). If you don't restart Minecraft after your Hardcore death loading into a world then crashes the game and no crash report is given, due to the game thinking you are still in the Hardcore world.