i am having a group of my friends play dnd but one of them wants to leave another for dead and idk if others want to do that to i don't want to ruin the other person's experience

Have a group conversation with every player. Bring this question up and ask them how they want the game to respect these ideas.

When someone is down for the count, do they have a say in whether they are saved from the jaws of death? If they are, how much weight does this get vs. any player whose character wants to leave them behind as corpses?

There's no universal right or wrong answer to this situation - but there's one that fits best for your table and group. Asking them (the players as a group) and letting them decide (if you have no strong opinions) will guide you clearly and, with any luck, avoid drama and hurt feelings. Conversations between equals really solve a lot of table questions.

Keep in mind that the decision to leave another party member for dead is often forced by the DM, not the players.

There are a couple of aspects -

1) Does one character not want to heal another that goes to zero hit points in combat? They want them to live or die based on death saves? Is this what is meant by "left for dead". This one rarely comes up since 99% of people want to get the other characters back on their feet during combat since they have 100% offensive capability even at 1hp. It is almost always better to help that character get back up. If this one is the problem then the players and DM should have a chat about expectations and role playing. Think about it ... would a character adventure with a group that doesn't have their back? That won't heal them in combat? No character I have ever played would choose to adventure in such a group and neither would most others.

The only time this becomes an issue is when ..

2) The party is placed in a situation where they have to flee because they will otherwise all die. The party engaged an opponent that is too strong for them. One of the party is already down. Do they leave that character to die? This is a much more morally ambiguous situation and it is set up by the DM giving the party a powerful opponent that they either couldn't defeat or where they were unlucky enough for the encounter to become a possible TPK. In this case, most parties would agree that it is ok to run away if the cost of recovering their friend is everyone else dying. It can make for some interesting role playing but it is important to remember that the DM has some control over the opponents and situations. Strong opponents should usually be foreshadowed unless you are playing a game where they aren't (which should be discussed at session zero and might make the players more cautious and the situation less likely to come up).

Anyway, depending on what sort of "left for dead" you are talking about, you should either discuss teamwork or the fact that the world could have challenges that are too powerful for the party so they may need to be cautious so that the situation where a party member has to be "left for dead" isn't common and becomes a dramatic plot point that everyone is aware could happen during the game.

P.S. If the party is roleplaying trying to decide whether to leave a party member behind then everyone gets input ... the one player wanting to leave them behind doesn't decide for the entire party. In addition, it is quite possible that some might decide to run while someone else decides to make a desperate rescue attempt ... that you will need to adjudicate.

One thing that a lot of newer players don't get is that just because their character could want to leave an ally dead doesn't mean the player wants to leave the ally dead. You can roleplay this situation making it clear that you want the character to be convinced otherwise, or you can come up with a justification for saving them yourself that still preserves your character's personality.

"Sverda turns to leave, but then hesitates. 'I'm not doing this for you,' he says as he grabs the paladin under the arms and drags him to safety. 'It's just going to be a lot easier to get into that vault with you behind me to take any arrows. But one word of this to anyone else and I'll kill you myself.'"

So you have established that your character is an antisocial jerk without you actually being an antisocial jerk. If you sit down at a table to play D&D, you are agreeing to a cooperative game where you play as a team. You need to do that as a player regardless of your character alignment.

I stay away from party's decision as much as i can. If the party want to leave a character for dead, i'd certainly encourage them to talk about it in respect of the player concerned, but in the end it would be their decision.

After dead, depending of the reason behind it, if i still want to save that character i can have anything happen to it after it's been left for dead.

Make sure they understand that just because THEY want to leave a character for dead doesn't mean their character does.

As GM you can't really do anything except have the party talk about it. You really should not force the issue one way or the other - it falls under player agency.

Quote from Wysperra >>

As GM you can't really do anything except have the party talk about it. You really should not force the issue one way or the other - it falls under player agency.

 Unless you need to arbitrate in event of unresolved disagreement. 

Do they have a reason for wanting to leave that particular character for dead?

Sometimes when a character is a prickly uncooperative lone wolf or a kleptomaniac who gets the party in trouble one of the other tropes that makes them a liability to the party, not saving the character is the party’s way to get rid of them. In those cases it might be best to just let it happen.

Have had  this happen on occasion. Here is what I did last time. I asked the played did they  want to continue. If "NO" then party leaves and player has new character enter pretty quick to be determined in story line. They can keep playing but maybe at a little disadvantage as they gave up all previous loot and items. If "YES" a God intervenes. Any God will do. You pick. The God revives the player and gives them something. Perhaps a stat boost. A slightly better armor or weapon than anyone else in party has. This can be a lesson for other members of the party. Perhaps down the road they will be in same situation.Perhaps they won't be afforded this same consideration. BUT now the player who was revived, now owes his new found God a favor in the future. This perhaps involves the whole party. As a thank you for that time they died...... Make it as SIMPLE as possible. This not only drags the game down as a whole but keeps group together and continues the mission at hand. Stop the argument before it starts. Worse case scenario. "Oooops I miscalculated damage. You actually have 1 Hit Point LEFT!!!"  

You're the DM? The player should follow their alignments...you don't have one good aligned person in the party?

let them do whatever they want, then tell the player who died that, congrats, they returned as a revanent(teh best kind of undead) and now get to try and hunt down the party

One of my characters died.
I do not take these things personally, I look at them as ways to play a different character.

But, the rest of my party did not know what to do about my death. They kept asking me as a player what to do. I kept looking at them and saying I am dead I can not give you any answers. (unless you could speak with the dead)
They totally forgot all the other spells our cleric had other than healing and attacks.
They forgot that two towns and just a few days away was a cleric who could raise me.
They forgot they even had spells to protect my body until then. Our cleric did not even look up the possible spells he could have cast the next day.

They thought I wanted to die since I would not tell them what to do. The DM know I could live, we were just seeing if the other players could figure out such a simple problem.

In the end they buried me. Unprotected, I came back as an NPC looking for revenge and looking to reclaim all my magic items they looted from my body. Other characters died before the rest even know what was going on.

After that adventure those new players figured out how to survive real quick for the next campaign. They went from a  pack of greedy murder hobos to a group that worked together to keep everyone alive.
They learned that a whole group of neutral to evil characters do not work well together in the long run.