The Delete World button on the Hardcore Death screen is not deleting the world after death. You are returned to the main menu, but the world is still loaded by Minecraft oddly (You can see that the world is loaded by going into options after you are returned to the main menu), and the world still exists on the list. (Reloading the world will still bring you to the HC death screen.)

Steps to Reproduce:
1. Create a Hardcore World
2. Die (Go into LAN and use /kill, fall into lava, get a creeper to blow you up, etc.)
3. The Delete World button should:
1. Unload the world from memory. (Similar to hitting "Save and Quit")
2. Delete the world from the world list and the computer's hard drive.
3. Return the player to the main menu.

However, right now, only point 3 is working. The world is not deleted, and the world is still "running", visible via the Options menu or when going to manually delete the world.

This bug has occurred when I was in LAN, and through normal play.