This is a large part of the reservations I have about whether or not Minthara will be a bigger player in the story, the hoops you have to jump through to even have her be alive at the end of Act 1 are significant.
You have to both choose the path of most resistance in siding with the goblins, you have to not rebuff her advances, then after that you have to succeed one or two persuasion rolls in order for her to not stab you in the back after.
In a list of characters that players a likely to never have more than one dialogue with, expecting Minthara to get a really fleshed out role in the story probably ranks as low as a Kisame Hoshigaki gaiden.
The thing is, that the persuasion roll decided to pass the whole sequence with non-lethal result for Minthara is laughably easy (DC of 1 IIRC) if you treat her well. In future, we will have also options to have basically guaranteed wins on DC rolls in dialogues (or less rng/static persuasion etc.), there was article about this on one of gaming news sites. Larian knows that it can randomly lock people out of playthrough option and they will provide an option for those who do not want to reload 20 times to get the desired dialogue line. I can post source here if you are interested.
She plays pretty significtant role in the "evil side" already. There is huge possiblity of the whole evil route being altered as Larian has acknowledged that they need rework and more options.
I'm pretty sure that neither her nor Halsin will need to die, even if we choose the opposite sides (knockout comes to the mind, or a surrender cutscene). Reddit was literally full of complaints about this and for a good reason. Those are 2 fan favourites, when it comes to NPCs and "rocks fall, characters die" isn't the best choice. It's here for now, because there wasn't enough of time for Larian to flesh out the whole storyline.
For now, there aren't just enough of opportunities for those characters to stay alive, if we side with their opponents. I do not think that your average non-metagaming and "non-murderhobo" would kill a surrendering character. Harming those who surrender is seen as evil not only in real life but also in games as well.
Some time ago I have made a post about the fact that act 1 indeed needs more interactions and possible routes, including the mentioned surrendering and knockout being properly recognized by the game; it was well recieved and gathered plenty of views. This tells you; that it's not only my point of view.
I wouldn't be suprised, if we could side with Goblins but do not kill the Tieflings. That makes it much more netural; because as we can see the druids besides few of them, aren't exactly the nicest people on planet. This was pretty common complaint on all kinds of Baldurs Gate 3 forums too (steam/this forum/reddit).