Killing Dror Ragzlin after talking to Minthara teleports Minthara back to her room. What I did was:

1. Killed True Soul Gut
2. Talked to Minthara (and saved Goblin Sazza) - Minthara left the room after this.
3. Killed Dror Ragzlin
4. Unexpectedly found Minthara back in her room after trying to kill some goblins stationed in her room (they shouldn't be there in the first place, since I killed the goblins around her room, even the scrying eye, before killing Dror Ragzlin).

I also noticed that going to camp (without even doing short rest or long rest; I just went back to drop the goblins' corpses to my Traveller's Chest), immediately progresses the Raid the Emerald Grove and Save the First Druid quests. Raid the Emerald Grove says that the goblins already left the camp, while, Save the First Druid says that I should notify Halsin about the impending attack on the grove.

Since I wanted to kill Ragzlin while still being able to witness the Grove Raid, I reloaded into a previous save wherein I went to camp (without doing any rest again) immediately after killing Ragzlin. After leaving camp, I noticed that the goblins outside Ragzlin's room are still hostile even though I killed him discreetly (which is practically a known behavior of goblins in the Goblin Camp), but Minthara's room has no one there. When I go to Emerald Grove, it behaves as if the raid isn't coming. But when I take a long rest, the raid starts.