After dying in singleplayer hardcore and choosing the delete world option, the main menu background disappears and the world still was displayed in the singleplayer menu. Choosing the world caused the entire game to go grey and become unresponsive. A restart fixed it, except the world was still displayed. Playing it that time put me back to the death menu, and choosing delete world caused the same to happen again. Spectate world works except for the chunkloading issues mentioned in other reports.