Don't know all that much about Hades II, never finished 1, but I'm gonna make a call:
Zagreus will fully embrace his role as the God of cycles. He will be the penultimate boss of the game and prevent Meloe from reaching Kronos, for one reason or another.
The two outcomes of this relationship I could see will be:
Zagreus will refuse to let Meloe kill Kronos and will be beyond persuasion. Meloe will have no choice but to kill Zagreus. Permanently. After doing so, Kronos will face an all-powerful and absolutely livid Meloe, possibly crumpling like wet tissue paper in a pyrrhic victory. Meloe, Goddess of spirits and witchcraft, will try to keep a part of Zagreus alive, a token if nothing else. The end of this Greek tragedy will see Zagreus be relegated as a forgotten and obscure God, as punishment for aiding Kronos.
Everything is actually chill. Kronos dies, perhaps with Zagreus's help. At the end of the game; Zaggy, as the God of cycles, will let Meloe replay a simulation of the game. For sibling shits n' giggles.
