I looked, the game really doesn’t talk about the loss of the soul, only Karlach says that she thinks that Astarion has changed, he is no longer the same. But I definitely remember the words about the soul, and then I thought, maybe I’m looking in the wrong place, I loaded into UAstarion, and there I discovered it, it’s Karlach again and she says: "He’d hate to hear me say this, but l'm so fucking proud of Astarion. He could've had it all, but he kept his soul instead". That's where it came from. The players who abandoned the ritual heard these words from Karlach, and decided, probably, UA saved his soul, which means AA did not. But this is disinformation. And just the opinion of one companion, who generally does not know and understand Astarion as well as Tav knows Astarion. And I also think Karlach is not talking about the soul in the literally.
Thank you! The history of the headcanon has been revealed! Karlach is our main ideologue against the Ascension. She's also hysterical after the Ascension that Astarion isn't the same anymore. Also, I saw some cartoon style animation where Tav is pouring snot on some chain, sees Karlach's ghost, then tries to set the castle on fire or something. And attempts to establish Astarion and Karlach as a romantic couple. And slogans about Karlach in the “She can fix him” series. She can fix the problem with someone who becomes illithid is all she can “fix”. But it's very interesting how they made a whole a priori statement out of one (!) companion's line, that it even caused anxiety and desire to find all possible information about Mephistopheles and pacts with devils... Karlach doesn't understand Astarion at all, she's an infantile and not particularly intelligent character, I don't even know which of the companions would suit Astarion worse as a couple, unless Will...
When I first encountered that line from someone, I too thought it was a metaphor and there was simply nothing more to say, in terms of concrete logical argumentation.
Originally Posted by Ametris
Sounds like a metaphor, not a literal description. The whole point of carving the scars on Cazador's back is precisely so Astarion doesn't lose his own soul. It's a trade and a loophole in the deal Cazador made with Mephisto.
Yeah, that's right. As an option - Cazador pays for the deal as a result, and the fact that he didn't get the power is not Mephistopheles' problem, the power was given. Another option is a “power in exchange for souls” contract, without any relation to the soul of the one receiving the power. This is more than logical - Mephistopheles gets 7000, that's quite enough. In that case, Cazador becomes one of the souls that Mephistopheles was paid with.
She's also hysterical after the Ascension that Astarion isn't the same anymore. Also, I saw some cartoon style animation where Tav is pouring snot on some chain, sees Karlach's ghost, then tries to set the castle on fire or something. And attempts to establish Astarion and Karlach as a romantic couple. And slogans about Karlach in the “She can fix him” series. She can fix the problem with someone who becomes illithid is all she can “fix”. But it's very interesting how they made a whole a priori statement out of one (!) companion's line, that it even caused anxiety and desire to find all possible information about Mephistopheles and pacts with devils... Karlach doesn't understand Astarion at all, she's an infantile and not particularly intelligent character, I don't even know which of the companions would suit Astarion worse as a couple, unless Will... 
