I first started by talking to Kagha and receiving a command to drive the tieflings out of the grove. I figured getting rid of tieflings would remove three whole fights, so I went to Zevlor and asked him to remove his people. He gave me a quest to talk to Wyll and do the standard "kill three goblin leaders" business, but I insisted about him having to go away now. This makes Zevlor attack, and needless to say he didn't live.
This is where the interesting things started happening. Afte reporting Zevlor's death to Kagha, she says you still need to remove all other tieflings, and it should be "even easier" now. That's a lie - no matter how many tieflings I tried to talk to, there was no option to make them feel unwelcome. Trying to purge them manually (I started from Arabella's parents) resulted in the druids acting like standard guards, and offering me a fine or prison. Clearly, the druids have no appreciation for the fine art of ethnic cleansing.
I decided to approach the situation from the other end, and kill druids first - or at the very least, Kagha. I did the quest about shadow druids in the swamp. The quest ended with Kagha and the shadow druids dead, after which I turned on Rath. This is where things turned from "interesting" to "broken". First of all, I noticed that Kagha's death failed to reflect in any way in my journal. Secondly, for some reason, neither Rath, nor his wolf reacted at all to being murdered, and I just stabbed them repeatedly as they just stood there.
After Rath died, I proceeded to start the purge on the outside. Curiously, only about half the NPCs turned hostile after being attacked - the other half watched the first half being killed. Far more curiously, I saw three tieflings inside the grove, speaking between each other as if the tieflings attacked the druids, and killed them all. Upon being spoken to, however, they had different dialogue - implying that the druids are in the process of attacking, and they fear for their lives.
After killing the druids and the tieflings both, I headed to the refugee camp, where tieflings stood armed. They also had strange dialogue that implied they're under attack by the druids. I killed them all, and headed to the Makeshift Prison - for some reason, every single tiefling civilian NPC was gathered inside. Probably, another result of the imaginary race war against the non-existent druids.
https://i.imgur.com/GiQqJPx.jpgHaving killed those too, I killed two or three tieflings by the gate. I then ran around the grove and the camp to make sure every single soul there was dead - which I had to confirm, because I did not have any journal entry I expected on the matter. Upon confirming it, I teleported to the goblin camp and spoke to Minthara. There were no lines of dialogue anywhere that allowed me to say the job was already done before it was given to me, so I agreed on the ridiculous plan of attacking an empty grove.
https://i.imgur.com/HjyTx4o.jpegNormally, you return to find the gate closed, and a cutscene plays where the tieflings open them for you and let you in. There, during the dialogue with Zevlor, you get an opportunity for betrayal. However, because Zevlor was already dead, and so were all other tieflings, no events trigger. I broke the gates with melee attacks, and ran around on top, even turning the now useless winch and blowing the war horn to see if it will make the goblin army spawn, but no such thing happened. The journal entry of the quest tells you to return to tieflings, so it appears that you absolutely have to have Zevlor alive for the army to spawn.
https://i.imgur.com/xFbxntQ.jpegtl; dr - if you decide to kill tieflings and druids out of your own volition, strange bugs happen. Zevlor being alive, for a bizarre reason, is absolutely mandatory for the "Raid the Grove" quest to proceed normally, and his death breaks it.
Fun fact - if Zevlor dies, he has a grave by the gates. You can dig up his body, and if you're a cleric, you also have some unique lines on the matter.
https://i.imgur.com/htBhlmY.jpeg
