Sunrise Hearts

• 1 Death reduces the player to 8 hearts.
• 2 Deaths reduces the player to 6 hearts.
• 4 Deaths removes Keep Inventory gamerule. Deaths not tracked beyond 4. On Sunrise, remove 1 death from each player.

Alternate config available in versions, do take a look.

You cannot set gamerule KeepInventory false manually with this datapack.

For multi-player: if one player is on 4 deaths, gamerule KeepInventory false applies to whole server. I've also not tested it :)

No config - barebones datapack.