Funnily enough, it's actually so badly hung together, design-wise, that this is maddeningly simple to circumvent and creates complete non-sequiturs. On my most recent playthrugh, when I tested the minthara branch briefly, I engaged went to her with Shadow, Lae'zel and Astarion in party, and helped Minthara assault the grove, then agreed to meet her there... I returned to camp, swapped in Wyll and Gale, who had not objected due to not being there, and not left me, and then went to the druids, where I promptly betrayed and slaughtered them, with Wyll and Gale standing alongside me, and then doing most of the druid-murdering heavy lifting, with narry a complaint from either of them the whole time.
That's a tough nut to crack - Larian is combining hand scripted, linear Dragon Age style narrative content with a free systemic sandbox. Those will be forever at odds. Perhaps, Larian should try to govern story content through some kind of reputation system to conpensate (like - reputation with Wyll for every grove NPC kill - so even if he won't witness the conversation, he would leave based on your actions. Or even action take against druid grove outside the quest), but with how disasterously such stuff turned out in Deadfire I suspect it could backfire even further. That said, Deadfire systems were still tied to conversation choices making the whole thing moot - and they didn't manage to react to players actions anyway (for example companions who would leave you if you refused to side with their faction, would still stick with you if you just murdered the whole faction instead). Maybe tying BG3 reputation to player actions would make more sense.
