This is a [+] thread.
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So I’m curious if hit points and death saves are also ignored for similar reasons. Since nothing happens if you fail three death saves, do they stay in the game? Are they tracked? Do you make the roll? If your character can’t die, why bother rolling?
What about hit points? If the end result of hitting zero hit points is ultimately nothing, why track them?
I'm guessing your basic issue with understanding lies here - you are saying "nothing happens", which is incorrect.
In all the games I've played or run that limit PC death, when you run out of hit points, fail your death saves, or otherwise hit the mechanical limit, you
fail, for lack of a better term. Your character is removed from the action. You don't get what you want. Your antagonist does get what they want. You track hit points and death saves because that's how you track that failure mode.
You ask "Why bother rolling?" Well, let me answer with a question - have the only way
YOU have ever failed been by dying? Is death (or specific avoidance of death) the only way you've felt anything? Have the only ways your life ever changed been through death?
No? Well, then there's your answer - there's a lot of drama to be found without death, but we still need to work through life - thus the rolls.
If you do track hit points, what happens at zero? Are characters unconscious until someone revives them at zero hit points? Are they out of the combat until it’s over? How does it work?
It varies from table to table. When I've seen or used it in 5e, when a character runs out of hit points, you do the normal death save thing. If they self-stabilize, they'll wake up with 1 hit point after everything is over, and have to deal with the situation as best they can. If they fail the death saves, they are going to remain unconscious until someone helps them, or we are off combat timescale and what happens to them can be narrated.
At that point, if there's nobody to help them, as GM, I make up something interesting. There's going to be difficulty - maybe they suffer some lasting mechanical consequences of an injury. Maybe they are in the hands of an antagonist, or whatever - it really depends on the character, and the situation in which this happened.
Are monsters also immune to death or are their hit points still tracked and they’re as gleefully slaughtered as in every other style of play?
Again, it varies. Where I've seen it, most of the time, nobody cares much what happens to the monsters, so we don't establish whether they were dead or unconscious. They are usually down, out of the fight and the scenario, and that's sufficient.
Finally, what benefit is gained by having no character death?
Generally? Increased investment in character personality development, reduced anxiety of loss, and reduced risk of having a really unpleasant play experience for the player, and reduced risk of having to go through the rigmarole of making up a new character and work them into the narrative.