Dying in multiplayer as a remnant systematically puts you in spectator mode, rather than respawning you as a spirit.

This mod is conceptually incompatible with hardcore mode, the whole point is to not properly die when you are killed. What are you wanting the mod to do that wouldn't completely invalidate hardcore mode?

In singleplayer hardcore, you respawn as a spirit a single time. You cannot regenerate a human body, and the game is over if you die while possessing a mob.