I've yet to see anything that would suggest the avernus ending ending is anything but a death sentence at best and just giving karlach back to zariel at worst. The minthara end of it is likely in the same vain or vibe of wyl going with her. But again the whole avernus ending while cool is for just a death sentence with a few more dead devils at the end of it. So heroic sure but not really desperate youre just going there because there isn't another option. Maybe larian meant for the avernus ending to shine a light on how futile it is to really try and save her given they made a big deal about adding "the ending she deserves" and just puts her right back where she was trying to run from. That's assuming she only dies in avernus and isn't taken captive by zariel again which is in my opinion far more likely.
