Act 1, Goblin Camp. Last weekend I took out the first bosses. This weekend I killed every humanoid there, with sneaking around from the Underdark waypoint, attacking everyone outside in 3 little fight, and then a huge fight after using the Goblin waypoint and climbing up under fire.
Left alive were only the drunk sleepers, the 2 human cultists first encountered near the Owlbear, and 3 low level goblins I missed - they showed up after the final battle with Minthara and 3 goblin bosses. Fighting from overhead surprise attack made that fight very easy.
(Oh, I forgot about the goblin non-Absolute in the cage. Maybe I should rescue him later.)
Anyhow, I theorized maybe if I annihilated her army, I could talk to Minthara and leave her alive for Act 2. Doesn’t seem to be an option.
I wondered about knocking her out with a nonlethal attack, but I couldn’t figure out where that option is? I suspect that might be blocked, just as Hold Person didn’t work on Minthara.
In the end, Minthara was fighting alone but got up to our sniper position above and nearly took down my PC before Lae-zel killed her with a a greataxe.
I had Lae-zel carry the body and put all Minthara’s gear in an Old Backpack (from the Phase Spiders of the Underdark) to give it back if we can revive her. Sad to see full NPC gear. Turns out a Revivify scroll said she isn’t a valid target. And Withers didn’t offer a choice of her.
So, I think she’s a full goner, but who knows?

Maybe Halsin or some Underdark Drow or someone in Act 2 can “save“ her. Or I needed to drop the body a Withers feet. Seems like 99% unlikely anything will work.
Alas, DM’d D&D allows crazy stuff CRPG didn’t think of. Old story: My players killed Drelnza, the boss monster vampire general at the heart of “The Lost Caverns of Tsojcanth” classic AD&D Greyhawk module. They had a Scroll of Resurrection, and after debate that it wasn’t her fault she’s a vampire, they used the scroll. She’s a significant live, non undead evil but murky NPC in my campaigns even now. Out of character, my players didn’t regret it and I appreciated giving me an interesting NPC.