I didn't expect the 15 years after Ariel would be a fusion of the original Ariel and one of Kumoko's parallel minds. That being said, it would explain a number of things, such as continuing as a demon lord and maybe continuing with the old plans (although that might be false to a degree). At the end of the day, Kumoko herself is stupid, so if she had merely replaced Ariel fully, it's kind of doubtful Ariel would exist in any form anymore. If there's still half Ariel left, however, that's maybe enough wits to keep going as a demon lord.

I also wondered before how Kumoko is so okay with the classmates killing each other 15 years after, but seeing how she sees the local humans as little more than walking exp potions, despite having saved Sophia, she might have stopped caring entirely along the way. If it's like that, I can't help but wonder how interesting an MC she is any longer.