... You do know the tieflings survive and have story in all 3 acts if the goblins leaders are killed, right?
If the tieflings survive the grove, they'll be ambushed going through the shadowlands. How many survive might be a factor. If you stop the rite of thorns peacefully, they aren't killed on the bridge leading to the village, they'll be ambushed in the shadowlands, same as if you had killed every leader.
There might be more iterations, but those are the three I've seen so far. So if you want the Zevlor betrayal storyline, and Minthara, you don't have to kill the Tieflings or the leaders, you just have to resolve the conflict between the druids and the tieflings so that they're not pushed out of the grove.
It doesn't actually make a lot of continuity sense, you can travel back to the goblin camp with Minthara, and no one really acknowledges it, but there you go.
Some. Some tieflings die in the shadow. The rest are save-able, and make it to act 3. As opposed to all dying in act 1.
