Vastly different character on my end (Githyanki necromancer), but apparently many similar decisions and also a first game (finished yesterday) with as little meta info as possible to keep the suspense and sense of wonder. Sava (profile pic) would have started lawful evil, but drifted more and more towards chaotic good due to all that happened at and after the Grove.

Like Orgon, Sava is also very intent on not becoming a Ghaik due to her being a child of Gith. As the group's tactician she also hated not getting all available information. When the "Risen Legion" attacked, it was like clockwork. The blinders blow, skeleton archers on the gallery, flying ghouls go for the mages and clerics, mummies in the back giving remaining threats stink eyes, then in with Lae'zel and Karlach dimension dooring from unprotected angles to dish out the pain. By the end of Act 3, Sava's idea of a good fight was to plough over the surprised opposition within two rounds without losing a hit point. This could only work with solid info. After making so many unlikely friends and meeting Omeluum, she could accept an illithid ally, but not being fed tailored shreds and half-truths only when the Emperor was beyond denying. Sava also hates being told what to do.

Sava was also able to withstand the astral tadpole* and could have forgiven the Emperor for lying about being illithid with three Githyanki (Sava, Lae'zel, Sina'zith) in the party. She even had to turn down the Emperor's romantic advances and thought they would finally see eye to eye. Then, over the course of Act 3, the relationship soured more and more. Orpheus being chained was Vlaakith's work, so Sava could accept the prism situation as necessary evil until the Absolute was defeated. What irked Sava to no end was that the Emperor kept turning every legitimate question, every disagreement into a trust issue. Here's where I would have loved the dialogue option "Dude, this is not what this is about AT ALL!" After helping Jaheira save Minsc, the relationship soured. Without the Emperor, at least some of Orpheus' honour guard would have survived. It hated Minsc for being uncontrollable, was a complete buzzkill when we went to the House of Hope for some quality hammer time, and with all the documentation we found on its previous involvement in the Absolute conspiracy, the Emperor began seeming more an more like a disgruntled control freak who was at least a part of the problem. Then, that whole Wyrmway tragedy unfolded. The premise of Lae'zel on a red and Wyll on a bronze dragon landing on the High Hall roof to announce that the apocalypse is cancelled, a beautiful dungeon so late in my playthrough, and then a huge (in-game) anti-climax that could have easily been avoided before a score of Flaming Fists had to go to the Healers' Wing with concussions, broken jaws and, er, thoroughly kicked buttocks, if the Emperor had just been honest for once before it's too late. Was Balduran a sun elf?! Or Kreia from KotOR 2?

The showdown in the prism was the final straw. ("My knight in shining armor?! Sorry pal, that was Lae'zel on that Nautiloid!") While there was not only the reasonable suspicion that the Emperor had planned it all along, there was no way Sava and Lae'zel would have let it consume the brain of Mother Gith's true heir, let alone hand over the Netherstones! Too often the Emperor had made bad choices for the group and they had to suffer the backlash. Sava's thinking was that losing Orpheus would doom the Githyanki to more centuries of tyranny, but that giving the Netherstones to the Emperor could result - by design or failure to wield them - in the Absolute taking over the multiverse. Now, it had become a trust issue.

Since Gale and Lae'zel were the last remaining companions with open quests, they were on the team when we went to the morphic pool. (The other companions were probably busy back at the Elfsong working on Wyll's rebranding and playing Balor Ale pong?) I had also brought Karlach since Sava had promised to stick with her until the end. Of course, I hoped there would still be a chance to fix her heart or otherwise keep her alive. After going through the options, Sava stepped aside for the true hero of Baldur's Gate - Karlach Cliffgate. Gale suggested thermal destruction, Lae'zel had a revolution to start and an egg to hatch. Sava, well, wanted to live. Seeing Karlach as a mind flayer was horrible, though.
This is exactly why Baldur's Gate 3 is such an amazing game. You really feel with the characters and endings like these won't easily let go of you. This is good narration! HOWEVER,...

Sava is a trained military leader (Soldier background).
"Oh, you want to leave the team and join the enemy?" The usual punishment for that is death. But with the camp now inaccessible, all undead thralls and elementals dismissed, and the events once again not unfolding according to plan, Sava would have loved to offer the Emperor parlay if Orpheus agreed. But could he really be trusted to wield the Netherstones and control the crown? Hey, maybe Omeluum hasn't reached the Underdark yet!

Perhaps I will revisit the option of a prince's sacrifice next time, but I must admit that some of the whole Blade of Avernus ending doesn't sit well with me coming from AD&D 2nd edition. In 5e D&D or at least in BG3, the banks of the Styx seem to be a place where mundane wolves have a chance to take on Baatezu and live. In Planescape, things would unfold exactly as Karlach says in the House of Hope. It's Zariel's (2nd ed: Bel) place, so staying in the House of Hope would make it a trouble magnet. Every stone will want to kill you. Not that it can, but it will want to. Wyll with drained powers and Hope don't make much of a party, let alone if an entire army of devils with a tactical target comes knocking. And even if they won, in the workings of the Outer Planes Avernus has to stay Avernus or degenerate into a fiend-infested demiplane while Baator spawns a new first layer, probably feeding on the Outlands and prime material plane locations that became too lawful evil. So, during this organic playthrough, Karlach became a mind flayer and Sava rode off into the credit roll with Shadowheart and Scratch. The owlbear went with Halsin who I thought would have a better hand at taming its tempers. I hope the Hallowleaf cottage isn't that far from Reithwin, through.

*I often explored alternative dialogue options with quicksaves, but apparently botched this one and had to either roll with
a ghaik-enhanced Sava
or replay a very difficult, but epic fight. I only noticed when the companions brought it up on what was the next IRL-day.