Complex sentence: Instead of being changelessly immortal, periodically, deities died and were reborn by repeating the events of creation, thus renewing the whole world, but it was always possible for this cycle to be disrupted and for chaos to return.
Split into simpler sentences: Instead of being changelessly immortal, the gods periodically died and were reborn by repeating the events of creation, thus renewing the whole world. But it was always possible for this cycle to be disrupted and for chaos to return.