Bug with the bandit lord quest

Hi all, I've got a problem with the bandit lord quest, I was with 2 friends who had already made this quest, but it was not my case.
So I talked to Oak, and it let us a choice, and a vote ( kill him or not ) my firends already had made the quest with killing him, but I clicked on help him, so they hit him, but they could hit me too, it was weird cause a first time they were killed by him, not me, so it completed the quest, but they come again, and killed him, and me after (cause we thought that had no importance), but now I'm block cause I need speak with Oak, but he's already dead and he doesn't respawn...
So now, I don't know what to do, cause my 2 quests need to speak with him and get the Apex, so I really need help for a GM or everyone who can help a little...

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Tifain wrote:

... but now I'm block cause I need speak with Oak, but he's already dead and he doesn't respawn ...

Mobs do not respawn in PoE.

Leave the area (portal to Forest town)
Click on the waypoint in town and then hold CTRL key and click on Oaks area, select new instance.
If you don't have the waypoint, yet, start from Vaal ruins.

Usually people kill all bandits for the skill point, but not always.
It's a good idea to ask in party chat if you're teamed up.

Yeah, thank you man :D