Her being fixed isn't necessarily tied to going to avernus because if Larian wanted to go for avernus dlc, they could just have her fixed but wanting to settle the score. What people think (and have reason to think so) is that for whatever reason, Larian didn't add an option to fix her and is so heavy on avernus ending because they go for the dlc where ideally we'll get our fix. Hence why they added all the extra lines where Karlach is totally hopeless, why they added the whole cutscene at the end and why they called it "the ending she deserves". You know, "avernus is the only hope but don't worry, dlc is on the way and you'll get what you want there"
