The new and improved limited lives data pack allows you to set a certain number of lives that each player can have before they die for good.

This does not work on realms? for some reason :|
Realms sucks big peepee? let me know in comments

• Works in single player (can break in multiplayer... make sure to /reload when all players are on to reduce bugs)
• you can reset it with /reload (deaths will reset)(lives will reset)
• if startup message doesn't appear use reload (deaths will reset)(lives will reset)
• Ability to change the number lives from 3 (default) to any number of lives by using/function lives:settings where Lives is a number between 1-∞
  
• Has startup and death messages
• Puts players into spectator mode upon death
• If you want to reset the game because everyone is dead for good I recommend using /reload

Version 2 is out and there is a small bugfix

• Sometimes score wouldn't reset when going from spectator back into survival via commands
  

To Uninstall this data pack run this command and then you can safely remove the data pack from the world folder: /function lives:settings, if that fails get the newest version from here and install that instead. To make sure you have the newest version and run /function lives:settings and as long as you are on the newest version it should work