Award XP for the types of play that you want to encourage.

RAW, XP is awarded for defeating / overcoming encounters, but it's left up to DM discretion as to what that entails.

Some (rare) groups will say that you only receive XP for monsters slain in combat. This avoids the problem of a 'recurring' enemy as you mentioned, but will heavily incentivize combat as the primary mode of resolving problems in your game. Playing with this sort of system, it probably won't be long before players start finding excuses to get in fights and to kill enemies even if there isn't a good narrative reason to do so.

Most groups would still award XP if an encounter was 'resolved' in a non-lethal way. This is very much customisable depending on what you want the major themes of your campaign to be. If you're playing a political intrigue focused campaign, maybe you award full XP for a non-violent resolution, but only a portion of that amount if they resort to violence. Maybe you're playing a survival campaign, where getting away alive is all that matters - in this instance you might award full XP for escaping/avoiding encounters entirely, and less if they dealt with it in a poorly chosen way.

The bottom line is, players will usually (although there are exceptions) adapt their style of play towards whatever type of resolution grants the most XP. Be warned though; over-incentivising a style of play that your particular players do not enjoy will likely lead to player dissatisfaction.

If you're in doubt as to what you want at this point, stick with awarding full XP for any time that the party was under threat from the enemies but were still able to defeat / negotiate / leave or just generally progress beyond the encounter. You can always tweak it later.

Re: your point with the recurring enemy, I would just say not to give the party extra XP for any enemy they've already been awarded XP for before if it's in a short enough timeframe (same or next session). Otherwise, you might have situations where a party deliberately looks to resolve an encounter peacefully and then looks to backstab their new 'friends' in their sleep for a second bout of XP. Ultimately, you know your players better than any of us do, and you'll figure out what works best for them with some trial and error. Good luck :)

Killing monsters is not a requirement for recieving experience.

The DMG states (emphasis mine):

Experience points (XP) fuel level advancement for player characters and are most often the reward for completing combat encounters.
Each monster has an XP value based on its challenge rating. When adventurers defeat one or more monsters-typically by killing, routing, or capturing them. (DMG p.260)

Thus, the party should get experience for successfully completing an encounter, no matter how they deal with the monsters. What constitutes "completing the encounter" is up to the DM. Additionally, awarding full experience for ending a fight with out killing all the monsters helps prevent a "murder hobo" playing style.

In your given scenario, it is up to you whether it counts as one or two encounters. However, the party should get 200 XP for each encounter. I would award the party 200 XP twice.

I was just thinking about this problem the other day. The solution that I allowed myself to accept was based on the idea of experience. These heroes are interacting with characters and challenges that make them more experienced over time, allowing them to overcome greater challenges in the future. I will give two possible solutions, the latter of which is actually a very old solution.

One is that you treat every encounter and challenge as a single instance of experience. While you might gain say, social acumen, by growing up with your family. There is only so much you can get by overcoming the same 'encounter' over and over again. If you left the nest thinking yourself to be a social expert because you've won the argument with your sister over how to divide the tv schedule for 100th time, you will quickly find that it didn't prepare you for the outside world. An encounter, once it has entered into some form of completion where the obstacle that encounter represented is no longer there, can give experience once (whether you want the experience to be awarded after the first instance, or at the end of the process is up to you, note that if players are tallying their EXP after every combat, they may suspect that the NPC's they scared away might come back if you don't award them the experience for that combat).

Based on this interpretation, I would consider the listed EXP on a monster to be all the experience they can provide to an individual over a lifetime, whether it is awarded all at once or not, whether it is awarded for combat or not.

A second possible measure is using some sort of gauge as to the success of the players as adventurers. Did the players get something out of finishing the combat or solving the puzzle? Sometimes that reward is not dying, at other times it is getting some favor or a sum of gold. Like the previous example, I can provide an irl justification for this method. If someone is very determined in their job to get more customers, and tries 30 solutions to do so, it is very likely that this person's understanding of the issue was fundamentally wrong. If experience is in fact practical wisdom applied to achieve a goal, then the achievement of goals itself is a direct measure of a character's experience.

For adventurers, a metric to consider would be the acquisition of gold - whether or not the character decides to take it or not. This is the method of gaining experience in Advanced Dungeons and Dragons, 1st Edition. If the players scared the goblins away, but aren't able to save the prisoner or find the treasure chest because the threat of the goblins are still there, and they've blocked up the passage - have the characters really learned something from the experience? (plenty of people would say yes, no worries, you wont offend me by disagreeing).

The solution I would propose is not a direct gold to EXP as was present, but rather awarding EXP for the encounter when the 'dungeon' or 'area' is finished and the players have their reward. The value of the 'area' would be equal to the total exp of the monsters and challenges within, perhaps with some bonus from miscellaneous goals or treasure. If they can talk their way through the goblins and stealth the goals and gold away from the hideout, then I would award the full exp value of the dungeon. However, if they are missing something, I would decrease proportionally.

Having tried this in the past, I settled on making a list of things present in the dungeon (treasure, plot hooks, macguffins, favors, information and other rewards), and giving players a letter grade based on how many they found - then rewarding that percentage of the dungeon experience (Complete=100% A=90%, B=80%, C=70%, D=60%, F=50%, E=30%, Abandoned=0%).

On a personal note, I am currently running a combination of Lost Mines of Phandelver and Keep on the Borderlands (where the Cave of the Unknown = the Cragmaw Hideout), I have been very simply awarding 1 experience point for each gold piece and experience points for each monster they kill or 'resolve'. Resolve meaning that that monster is no longer relevant in any way to the game, and wont come back, appear, or even be present if the players choose to come back to an old dungeon. In all 3 cases, I would award EXP for those goblins only once.

Espero que ajude!

The reward depends on the encounter and expectations.

You can base XP on what happens.

If you just reward them for killing, that’s all they’ll do.

EXPERIENCE POINTS

The number of experience points (XP) a monster is worth is based on its challenge rating. Typically, XP is awarded for defeating the monster, although the DM may also award XP for neutralizing the threat posed by the monster in some other manner. (MM pg. 9)

4 goblin encounter worth 200 XP for killing them, not socializing.

You can however adjust XP based off what was accomplished.

• %XP based off kills
• %XP based off RP
• %XP based off creativity

Did they kill half the party .. 100 XP

Did they use a skill / RP to get the rest to run off .. 50 XP

Did someone do something creative .. 25 XP

Not only are you rewarding for what they did, but also create an adventure hook, for when the goblins return with friends.

You don’t want to penalize the hack & slash players nor leave out the role players.

I would have awarded them xp for de-escalation first, but then if they blatantly did anything they could to kill them then no sorry, you get no extra XP for killing them afterwards. But if it was a separate encounter later on where the goblins attacked of their own choice, I would award XP for the fight.

I find it tricky and you have to adapt it. In the Mina Perdida de Phandelver adventure, if you follow the milestones, they won't level up to 2 until you get to the end of Cragmaw Cave, which is the entire first chapter! On the other hand, if you use XP, after dealing with the 4 goblins at the start followed by the 2 lookouts outside the cave (50 XP each), since they only need 300 XP to get to level 2, that would make them level 2 before even getting into the cave! By then, completing the cave that would land them with another 800 XP so completing the cave should land them on level 3?