As far as i know Kagha only speculates that Tieflings would surely pay your for your help ... i wouldnt search for anything deeper than that.
Kagha's request to offer to lead the tieflings out of the grove seems to suggest that there is a possibility of you leading the tieflings into some kind of ambush
Here is your misstake.
Kagha suggests you to lead them out ... bcs that is what she want, she dont care how possible it is, you were just told to handle that, its yours problem now.
When you talk to Zevlor ... or rather, when i did (it is possible that we picked different dialogue choices and you discovered some shortcut, dont really know without screenshots) ... he specificaly states that they WILL NOT LEAVE UNDER ANY CIRCUMSTANCES until Goblin threat will be dealt with. Ok, hes using different words, but this is basicaly his message.
So as you keep pushing him, it makes sense that he become hostile ... but i agree there should be dialogue option to say "fine, have it your way ... coward" or something like that, there is really no reason for *dialogue choice* if you have only one.
But no, as Zevlor say there is no way they would ever leave the Grove unless Goblin leaders are dead ... so, no chance to lead them ... well, anywhere.
Basically, I'd be thrilled to boot the Tieflings, let her seal the grove, and be on my merry way.
Well, if this was your goal ... then you were on right track.
If you kill Zevlor, report it back to Kagha, and then Long Rest (i strongly advice doing it OUTSIDE of the Grove ...
The Grove will get sealed ... Tieflings will be gone ... and all druids inside will become hostile.
There is (at least curently) no reward for this approach, and you cant then side with Goblins, bcs Minthara will be pissed that bcs of you she cant massacre the Grove as she wanted to.
So your only way then would be side with very depressed Halsin, but you can leave Goblin leaders alive, bcs he no longer cares if they die or not!
But it is possible!
