Consider this entire post a spoiler I guess. It is mostly hypothetical, but it is about Act 1 and Act 2 events.
I started writing this as a reply to another thread, but it took a life of its own! Hopefully this is a different view on a very commonly raised issue, although I have read very few discussions in order to avoid spoiler.
First things first, I haven't tested this, but I am pretty sure that the route you take through Act 2 is not determined by how Act 1 played out. So you can still go to either Last Light Inn or Moonrise Towers first and follow their storylines from their perspective. I assume that you would be able to defend the Grove but then show up in/infiltrate Moonrise and do their quests. If you go to Last Light first and work with Halsin, that would be a better a better point to lock players out of recruiting Minthara, if there must be a lock-out at all (make Minthara unrescuable once the player has reached some early point of Halsin's quest).Story-wise, it fits very well to be able to recruit Minthara after having defended the Grove from her.
Even if you successfully raid the Grove,
Minthara's mission is a failure and she is about to get executed when you meet her in Moonrise.
You also find out that her actual mission was to retrieve the Artifact, not necessarily to wipe out the Grove. She was even somewhat reluctant about the mission, since she had to work with a goblin army, and it's not like the goblins were suited for anything other than wanton slaughter. It is quite clear that, had Minthara had complete control over the operation, things would have played out differently - though of course she would just as well have zero qualms slowly torturing every last living creature in the Grove if that was needed to get the mission done or if the Absolute demanded it.
Given Minthara's attitude towards the goblins and towards her mission, and her character in general, it makes sense that she would not throw away her life for a flawed and lost cause but she would rather retreat from this particular fight. She would rationalize living to better serve the Absolute another day.
Having completely failed, she will of course still end up being tortured and erased in a most inhumane way.
A forgiving player character could see a redeeming quality in those points, and less-than-forgiving origin characters can still leave the party over recruiting Minthara. Having an argument in the party right in Moonrise Towers, possibly in the throne room, sure makes for an exciting situation to resolve. Halsin might have a thing or two to say (or slay?) back at the camp.
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This part optional: Ok, I got
a little super carried away with a potential confrontation with party members over Minthara. What if Halsin himself is in the party when you go to Moonrise? Now we are getting in completely new content territory and I am basically writing fanfic, but I decided to roll with it and keep writing. DE maybe

?
In the following scenarios, Halsin and Minthara remain mutually exclusive as party members, but there is more player agency, and some more exciting situations to find your party in. If this specific confrontation happens, the player is also locked into either the Moonrise or the Last Light ways of resolving Act 2, depending on whether Minthara or Halsin ends up alive.
So you have Halsin with you, you go to infiltrate Moonrise, and Halsin starts a fight then and there if you attempt to recruit Minthara (or even if you show any empathy or forgiveness towards her).
Possible outcomes for this:
- Fight happens in the dungeons:
- You are forced to kill Halsin, a few Moonrise guards, possibly certain other party members if they side with Halsin. Going back to the Throne Room, Ketheric finds this amusing in some way, he allows you to keep Minthara, and you proceed with the Moonrise storyline.
- You knock out Halsin and take him with you, so you can't take Minthara. Going back to the Throne Room would be a bad idea in this case. Find a way to escape, and be prepared for some good rolls at the camp if you want Halsin stay with the party.
The intent: So you screwed up somewhat. You should have seen this coming, really. Things could go bad, but the situation is still salvageable if you keep a cool head.
- Fight happens in the Throne Room:
- Halsin is hostile, the guards are temp hostile, but the more important NPCs are neutral and not taking part. Minthara is held in place and not allowed to take part. Ketheric lets you fight for a turn or two without interfering, but then he steps in and punches a hole through Minthara's chest. This is your cue that you screwed up, and also that you can't win this fight. One of the characters, or the player's Guardian, should very strongly indicate that fleeing is the only option. Halsin is not under player control, but he will attempt to escape (and players can sure still help him). If he makes it out alive you get a scene at the camp, with some difficult checks to have him stay.
- As before, but you manage to kill Halsin before Ketheric interferes. Since you were willing to kill your comrade for this, he allows you to keep Minthara and follow through with the Moonrise quests if you want to. Ketheric pretty much sees you as a pawn.
The intent: You screwed up a lot. You were inconsistent and inconsiderate in your motivations and your choices, and you got into a serious conflict with your own party. This puts you in a much harsher predicament, but you can still resolve things one way or the other if you can stay alive. It is quote possible to lose both Halsin and Minthara, in fact this is the more likely outcome. Face the consequences of your actions!