The key difference is exactly that, with a further distinction that having eternal afterlife and life makes one afterlife the thing that matter, and life a transient, childhood like state which doesn't really matter at all. When we played cops and robbers, it didn't matter when a child said "boom, you're dead". Because we just fell down, said "argh!" and five seconds later, we'd rise again and resume playing. That's exactly what death amount to in this scenario, with the added twist that your behaviour determines where you finally get. Better not fail that test! Morality would certainly develop very differently, with consideration for life being much lesser than they would be naturally. In the context of the OP's stipulation, Good implies concern for life, so it would be a dictate of the Good gods to force people to live their life to their natural end, because it's the Good gods preference, not because it's "real-world good" not to kill (= relocate to a better place) people.
(Muscular Neutral could posit they oppose Good not on the basis on being bloodthirsty monster, but because they want the liberty to end lives too miserable to be lived, aka euthanasia, without being sent to metaphysical Antarctica for that).
The importance of moralty itself would be questionable. When playing cops and robbers, the child aren't evil for playing robbers. Children aren't villains because they pick robber, in a world where life is a temporary, near insignificant time compared to eternity, Evil and Good could be Red and Blue, arbitrary and ultimately unimportant denomination for gods, the only things mattering being if you get to the Good Place in the end.
The existence of afterlives really creates lots of conundrums.
If Good gods grant Tahiti and Evil gods grant Antarctica, which is a classical proposition of monotheistic religion, the message is clear, one is clearly incentivized to serve the Good gods, because it would be ludicrous to pick Antarctica. In a monotheistic setting, it's OK because it incentivize to follow the rules set by the (only) God and societies' rules which align exactly (because noone want to go to Antarctica). In a polytheistic system common to D&D settings, the Evil gods would very quickly lack any follower except fools. And Good servant would be very unkind not to help fools to achieve the better outcome. If small faults would lead to be considered one of the False, and denied Tahiti, then actually killing people before they can sin is certainly something that would be logical, and even charitable to do.
If both Good and Evil gods grant their own Polynesian island, then, since life doesn't matter, the only thing that matter is how one adheres to the tenet of the god of his choosing (or the god he's raised into), irrespective of morality. It gives a very different meaning to Good and Evil. So for example, there is often a discussion about whether it's sensible to have an intelligent species that is aligned "always Evil". If being Evil and partaking in murder of an innocent, for example, was a sure way to get to their particular Tahiti), and "not illing an innocent" was mean being sent to Antarctica, then I'd say that they would be under great pressure to kill innocent. Which shed a very different light on their "always... alignment". Few of us would refuse to shoot an innocent if we had a gun pressed against our head (most of us will claim they wouldn't, because they are comfortably typing on their keyboard in the safety of their own home, I guess...) So unless the Good gods accepted the conversion (and sent to Tahiti) people who would convert after leaving an Evil life, basically everyone baptized into an Evil god would be under extraordinary duress to act Evil. Acting like this would be basically "eternal self-preservation". And if Good gods accepted conversion, then the paladin converting the evil baddie in the aforementioned scenario would be righteous (saving a soul by getting it to Tahiti WHILE removing a person that would otherwise need to be Evil). Even if it's a baby.
The existence of an afterlife would totally change the definition of Good and Evil to the point that alignmnet-Good and alignmnet-Evil are just tags to determine if one gets additional damage when hit by a Smite Evil spell, rather than the conventional sense of these words.
There are other possibilities, like both Good and Evil gods granting Antarctica -- all huuman races would probably try to unite and research heavily in arcane magic to get hold on a local variant of the Karsus' avatar spell and replace those oppresive gods -- an interesting setting to play in.
If Good gods granted Antarctica and Evil gods granted Tahiti, then it would need to be the epitome of altruism to be altruist. Not only would one get nothing from their kindness -- thatt's the concept of altruism -- they'd on top of that forfeit their immortal soul.