When you have died in hardcore mode it is possible to "resurrect" yourself due to the new spectate option. After you have died you need to click on the spectate option then from the pause menu (esc key) click open to lan. From the open to lan menu change the gamemode to survival, allow cheats and click start lan world. Finally when in-game make sure you are close to the ground (but still above it not inside of it) then press the "/ key" and type gamemode 0, hit enter and you are back into survival hardcore mode.