Here are a few thoughts I jotted down after a quick re-reading of book 16
The effecting of the deaths of Homeric hereos is surprisingly complex at times(even if the action is described in terms of mere butcher's work ,e.g.
'..it struck him where the head springs from the neck at the top joint of the spine, and severed both the tendons at the back of the head.'
In the poem there are hidden layers of both Olympian and earlier religions. For example the conflict between the wills of the various gods , (most of the heroes have a god or nymph in their lineage so there is a conflict between the various gods warring for the fates of their own offspring. There is also a conflict between the will of the gods and a higher fate which is preordained for each hero . The key passage on the death of Sarpedon seems to me;
'The son of scheming Saturn looked down upon them in pity and saidto Juno who was his wife and sister, "Alas, that it should be the lot of Sarpedon whom I love so dearly to perish by the hand of Patroclus. I am in two minds whether to catch him up out of the fight and set him down safe and sound in the fertile land of Lycia, or to let him now fall by the hand of the son of Menoetius."
And Juno answered, "Most dread son of Saturn, what is this that you are saying? Would you snatch a mortal man, whose doom has long been fated, out of the jaws of death? Do as you will, but we shall not all of us be of your mind. I say further, and lay my saying to your heart, that if you send Sarpedon safely to his own home, some other of the gods will be also wanting to escort his son out of battle, for there are many sons of gods fighting round the city of Troy, and you will make every one jealous.'
So unlike the Gods of today's monotheistic faiths, the supreme God of the Greeks was not all-powerful,though both in the death of Patroclus and Sarpedon he seems to weigh up his judgement as if he has the power to defy fate but must not do so. This seems to me a fusion of 2 religious traditions and the poets uncertainty as to how 2 immovable forces i.e. God and Fate can be reconciled. This adds to the tension and complex interest of the poem. The ways that these 2 forces interweave in the battle scene is very strange and complicated . For instance though Hector is not a coward Zeus can put 'cowardice in his heart' if it suits his plan at that moment . Likewise he can send other gods to assist as if that was a way of intervening without directly defying fate himself.
Another factor is that death is brought upon the warriors by their own success. The are not like Christian Knights punished for their sins or wicked actions but specificaly for overstepping the rules which bind mortals. By becoming too glorious and causing envy in the gods. Either by taking arms against a god or for going beyond an oath they took (thus Patroclus goes too far in his pursuit of Trojans. He is punished for disobeying the injunction given him by a greater power, a common folklore theme e.g in the myth of Orpheus when he looks back though told not to.)
So although Zeus cannot save his son Sarpedon from his fate he can ensure a noble passage to the afterlife where a parallel if insatisfactory form of existence goes on. He sends Apollo;
'Apollo obeyed his father's saying, and came down from the heights of Ida into the thick of the fight; forthwith he took Sarpedon out of range of the weapons, and then bore him a long way off, where he washed him in the river, anointed him with ambrosia and clothed him in immortal raiment; this done, he committed him to the arms of the two fleet messengers, Death, and Sleep, who presently set him down in the rich land of Lycia.'
) now i'm not asking for an essay to be written of course! just some hints 