been rewatching lyst and in doing so i had this realization about the show's cycles and patterns through the lifetimes -
chu kong follows a pattern of living on after losing xiangyun. it's not even intentional, like after losing cang hai he had his memories wiped, and then after losing song xiangyun as lu changkong, he had promised to stay alive. so unless they die together or he dies first, if any version of chu kong loses any version of xiangyun, he will continue to live. xiangyun on the other hand, never survives without chu kong. of course there's the third lifetime when she, as xiaoxiang, kills herself upon his death. but even from the second lifetime, she says to her parents that if lu changkong dies, she will die too. so unless they die together or she dies first, because there is nothing stopping her, any version of xiangyun will follow any version of chu kong to death.
but then, at the very end when chu kong gives up his life to save xiangyun through the soul protecting spell, xiangyun lives. she doesn't immediately sacrifice herself and has faith in his return, thus breaking the pattern just like they broke the time loop. every cycle is closed, and that's how you know they'll finally have their happy ending.