I haven't read through the whole thread, but my read on the situation in regards to the Goblins VS Druids is that the the Goblins and the followers of the Absolute didn't specifically have anything against the Tieflings, only the fact that there was a Druid circle there.
There should be an option to agree to escort the Tieflings out of the Grove (as in, hide them somewhere like the crypt after you clear it out), then side with the Goblins/Minthara in exchange for your own and the Tieflings' safety, and/or going with the angle that you want to teach the Druids a fatal lesson for treating the Tieflings the way they did. My impression is that Karlach and Wyll would be far more concerned about the Tieflings, though you'd still suffer a massive reputation hit from them for agreeing to help the Goblins take out the Druids, but I don't think they'd leave the party over the Druids dying as opposed to the Tieflings being slaughtered.
This way, you don't have to trade 3 companions for Minthara, the actual choice would instead be between Minthara and Halsin, which would make the tradeoff much more equal from a gameplay and narrative standpoint. This also gives you a way to resolve the whole situation yourself while keeping Karlach and Wyll, rather than grabbing Minthara and then just proceeding to the mountain pass, which feels like a metagamey exploit rather than something actually intended.
