In the current Early Access Build I am playing (4.1.1.2154614), I went through a long and exhausting fight against a green hag, at the end of which she surrendered. I negotiated with her to save her victim and let her go, and I got nothing mechanically from doing that. At least, nothing I wouldn't have gotten from also killing the hag, who was left with 12 hp. From a mechanical perspective, that means there's no reason not to kill the hag or anyone else who surrenders to you. I felt like I was cheated when I didn't get XP for defeating her. Had I chosen to kill the hag rather than accept her surrender, I would have gotten the XP and the quest would have continued and I'd have been able to loot not only the hag's lair but also her corpse (but that's something you give up for story reasons if you accept a surrender, and if you're willing to do that then that doesn't seem like much of a sacrifice anyway).

I defeated her, the fight ended in a victory for my party. What difference does it make if the monster is actually dead or not? I like that surrender is an option for NPCs, and that my character is less monstrous if they accept a surrender from a defeated foe. I like that my character does not technically have to be a murder hobo. However, there are enemies (more than not) that do not surrender. So for a big boss fight especially, not giving XP as though the monster was killed, feels bad. It's not fun.

Maybe this is something that's planned to be fixed for the future, but if it's not then it ought to be. I don't expect XP from every little dialogue interaction, but I do expect XP from defeating a powerful foe.

To get into the D&D5e rules as written, I'll share this little tidbit from the Dungeon Master's Guide (p160):
Quote
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 - they divide the total XP value of the monsters evenly among themselves.