I only just finished my first organic (no guides/spoilers) playthrough and
wound up with a turned Karlach. Yes, tough choice and great narration, seeing this is apparently the only way to save a friend from burning up in the end. I had hoped that after Saving the Gondians, Zanner Toobin would come up with an idea of how to fix her heart. By now, I read about how you can follow that whole Blade of Avernus arc which however was really a bit goofy to my taste. A level 1 ranger, a crazy cleric and Infernal Enemy #1 against legions of devils in hell?! Karlach said it at the House of Hope: They wouldn't stand a chance in the first layer of Baator I know from the original tabletop game. Or perhaps Wyll meant Avernus in Tethyr and he was just lost in the woods for a few months? I guess I'll give this ending a chance someday, if it's available with a pact-broken Wyll. Still, silly ending for an otherwise cool story arc and awesome character. The way we wound up in the prism, Karlach didn't want to go back to Avernus, so that was that.

Playing a Githyanki necromancer with soldier background would have left me no option, but to fight and kill the Emperor on the spot for treason after announcing he would join the Absolute. But weakened as we were, no way back to camp and stripped of all thralls, elemental and undead, his escape is explainable. After Act 2 and having met Omeluum and other unlikely allies, my Tav actually tried to befriend the Emperor, but the relationship soured over all that occurred in Act 3, because of him being skimpy with information about his hit-and-miss plans, which ironically turned his apparent trust issues into a self-fulfilling prophecy. After the Wyrmway, my Tav plotted to get rid of him at the earliest opportunity, although not necessarily killing him. (I actually spent a scroll to protect the unconscious Emperor on top of the Netherbrain to protect him from Nautiloid bombardment.) Therefore, an option to work with both Orpheus and the Emperor would have been nice.

The idea of running back to the Lower City and getting an illithid that is actually cool to handle the Netherstones occurred to me on the spot. Omeluum didn't seem like much of a courageous fighter, through. Maybe it wasn't up for the task.