For my novel the gods of the different pantheons have different kinds of immortality like in the Riordan universe but they will also all be killed in a few similar ways for my novel. Most of this is straight off Riordan wiki. I'll update it more when my comes in contact with others.
Ways for Greco-Roman Gods/other immortals to die in this universe:
Void of Chaos: Chaos is believed to be one of the few things able to truly kill an immortal (possibly by permanently absorbing their divine essence with it being impossible for it to ever escape), as Zeus held Hera over Chaos after her rebellion, threatening to drop her into the void.
Tartarus Essence Absorption: The infernal Lord of the Pit Tartarus has the ability to suck beings into the swirling whirlpool of darkness on his face, which he did to the immortal essence of Hyperion and Krios. In that sense, Tartarus can technically "kill" gods, Titans, and giants by absorbing their immortal essence into his armor for very lengthy periods of time.
Magic: According to Apollo, magic to destroy a god is entirely possible if they are powerful enough, provided their victims are weak enough to be overcome. Magic also can drain a god's power and immortality and granting it to someone else.
Immortality Revocation: Zeus has shown the ability to revoke the immortality of his fellow gods and turn them into mortals, having done this three times to Apollo. However, in Apollo's case, his powers appeared to be bound more than stripped as he still had bursts of godly power. In addition, when the Titaness Calypso left her prison island of Ogygia, she lost all of her powers, including her immortality, leaving Calypso as an ordinary mortal girl.
NOT SURE HOW THE ONE ABOVE WORKS. FOR THE SAKE OF MY NOVEL THIS IS HOW IT'LL GO. IF THEY HAVE HAD THEIR IMMORTALITY REVOKED, IF THEY COME UNDER A DIRE/ LIFE THREATENING SITUATION THEY IMMEDIATELY GET THEIR POWER BACK.
Ways to kill all:
Draining of immortal essence like Tartarus
Stripping a god of their divinities, effectively making them mortal once all their divine energy is gone
The immortality of Egyptian gods:
Killing and Duat Banishment: Egyptian gods can be banished back deep into the Duat either by being killed, which is possible, or by ensnaring them through very powerful and effective magical items such as the Seven Ribbons of Hathor. A magician can also banish them through certain spells that require their secret names or through execration. However, they will eventually return, as killing a god just kills their mortal body and drains their power, and the banishment will eventually end.
Shadow Execration: Gods can actually be permanently destroyed if a magician casts an execration spell on their sheut. According to Carter Kane, this is because if a person casts no shadow at all, their existence is meaningless. Destroying a sheut cuts all ties to the mortal world that a being has as well as the fact that the sheut is an important part of the soul. This is used to destroy Apophis, though it takes the combined power of Carter and Sadie Kane as well as Horus and Isis to do so without Carter and Sadie being destroyed in the process. Gods keep knowledge of this secret so it can't be used against them, as a magician threatening to execrate their sheut is effective blackmail against them.
Dependence on Ra's Life Force: If Ra the sun god is missing, the gods start to lose power slowly. Worse, if Ra is somehow destroyed (via shadow execration, for instance) all the other gods are destroyed as well.
Energy Depletion: Bast mentioned that it is possible for gods to cease to exist if they expend too much energy without stopping to rest. However, this is clearly quite a lot, as Bast and Apophis dueled continuously for thousands of years nonstop but did not cease to exist.
Norse Gods are perhaps the most vulnerable of all. While being beings of great power and are seemingly unable to die from old age, they are able to be killed quite easily by other gods, monsters, and even mortals (Kvasir was killed by dwarves). Norse deities enter the underworld when they die, and can be returned to the land of the living (as is the case for Baldr and Kvasir). Almost all the Aesir are destined to permanently die during Ragnarok.
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