MAJOR SPOILER WARNING
Do not read if you haven't cleared Tsukiyomi.
I actually didn't like the Yotsuyu and Goestsu arc personally. I believe their story should have ended at Doma castle and that we should have gone from there as I believe that it would have been the perfect ending to their respective stories.
Yotsuyu crushed by the castle of the nation that she tried to crush, dying in the depths of despair of her failure with absolutely nowhere to go and she receives terrible death as punishment for all the terrible things she did. Meanwhile, Gosetsu sacrifices himself to save Hiei and the WoL thus completing his own character arc of seeking an honorable way and place to die, finally able to be at peace knowing that he at least dies with honor while Yotsuyu dies dishonored and shamed.
In my opinion there was no better way that their stories could have ended, what would have made it even better from there is if they found Gosetsu's katana in the water and brought it to Hiei who could then wield it as he took all of Gosetsu's lessons to heart and became the new mentor/teacher as Gosetsu was to him and create a new era of Doman samurai. That would have been the perfect end to Gosestu/Yotsuyu and I'm not pleased by the way it was handled ultimately.