So me and a group of friends have a private server with a very limited amount of mods on it and when someone get's knocked out they are invisible to everyone else and unable to be revived. Running on 1.16.5 and the latest version of Forge.

Other mods used:
Beekeeper, adds a villager that trades bee related items.
Happytrails, the ability to make roads that speed you up.
Morpheus, a vote to sleep mod.
Regrowth, a mod that makes villagers add torches and fences around villages over time.
SaveYourPets, a mod that allows you to use bandages on pets to revive them.
SwingThroughGrass, a mod that allows you to, well... swing through grass with swords.
Tenshlib, a master for other mods.

Have yet to try it with ONLY hardcorerevival on, will update shortly when that is tested.