At the climax of Season 1 after the Tiān Xíng Jiàn is removed revealing that Yāo Tú Lí was sealed under it and Miè Tiān Hái leaves with the sword, we see Xíng Hài remain behind performing a ritual to fully awaken Yāo Tú Lí. when it does awaken the mountain that the shrine was on is destroyed leaving a creator.
We see the fates of mostly all the main characters by the end of the season but Xíng Hài is the only one that doesn't seem to be accounted for, so what happened to her?
Xíng Hài is alive. she is hinted at in the second part to Seishi Ikken as being the one who the Xuán Guǐ Zōng remnants contacted who made it so that when they die their blood would turn into acid (a spell Xíng Hài mentioned in the first season)
However she makes a proper appearance after the credits of the final episode of Season 2 where Huò Shì Míng Huáng, talking about Xiē Yīngluò's failure to get the Sorcerous Sword Index from Shāng Bù Huàn and how the organization may need to lead an invasion into Dong-Li to get it. it is then that Xíng Hài appears stating she is a messager from the demon world and proposing that Huò Shì Míng Huáng's organization accepts the assistance of the Demonic Armies for their invasion