Reacting to the player's death and turning them "undead" causes all kinds of compat issues with mods that also deal with death, as well as occasional sync issues. Since it's so hacky it's also more likely to break between versions.

Instead, Hardcore Revival should trigger once the player would take lethal damage, and keep them on half a heart in a K.O. state. We'll also have better control over the actions players can take while K.O. and everything should be so much better than this hacky mess right now.