Board Thread:General Discussion/@comment-30390828-20161120192150/@comment-13682699-20170728015403

Charas Soul was absorbed by Asriel, which linked them together through their Souls. When they turned to dust, the Soul had broken as well, rendering Chara's Soul unattainable. If it had stayed around, I'm sure that would have been noted during the recap of events by the monsters and their parents would have likely had a better time coping with the loss as they would technically still be with them in a sense.