The Lost Light
[this is the old 4e info, but it should still work for 5e]
Feywild – The Feywild has remained largely unchanged, and is thus considered a safe haven for all creatures. In the years following the death of the gods, hundreds of immigrants began pouring into the Feywild, searching for a new home. The eladrin and the gnomes, fearing the corruption of their beautiful realm, began to impose prerequisites before anyone could enter. When these were met with hostility, the Fey Wars began, and the eladrin, gnomes, and other fey creatures took it upon themselves to send all immigrants back to Khalin, and then to seal up the massive portals linking the two planes. They were ultimately successful, though with heavy losses on both sides, and today, the Feywild can only be accessed through one portal, located on the top floor of the Diamond Tower. Persons attempting to enter the Feywild must have proper business in the realm, and must also have the signature of one of the Lords or Kings of the city-states of Khalin. Even then, entry is only allowed for one week, unless for extenuating circumstances.
Shadowfell – the Shadowfell is, for lack of a better term, crowded. Millions of dead from across the multiverse settle here, before moving on to their final fates (if they ever do at all). These ghosts have set up hundreds of their own city-states, making the Shadowfell largely devoid of any living creatures, save for natural denizens of the plane. However, the undead that plague Khalin are not created here: the ghosts and other undead of the Shadowfell are for the most part neutral to the plight in Khalin, and don’t necessarily want to harm anyone from there. They have also begun a campaign to seal off most of the “cracks” between the two realms, but unlike the Feywild, there are many more portals to the Shadowfell, most hidden in the darkest of dungeons, and thus the ghosts are unable to seal them all. For this, the inhabitants of the Shadowfell are largely unwelcome in Khalin, as most Khalinites believe that the Shadowfell is harboring many undead liches and other guardians of the undead. Thus, the two realms share an uneasy truce.
The Astral Sea – Following the death of the gods, the Astral Sea has become a graveyard. Legend states that when the gods were destroyed, their essence coalesced into enormous, plane-sized stone versions of their avatars. The rumor is that these stones float through the Astral Sea, awaiting powerful adventurers to venture inside tunnels created by the gods themselves before their death, to reach the center and somehow give life back to them. Unfortunately, such a goal has not yet been attained, as most portals to the Astral Sea (which were rare to begin with) died when the gods did. Realms within the Sea that were once powerful strongholds of good and justice are now broken, a shell of their former selves.
The Elemental Chaos – One question asked after the gods died was, “What about the primordials?” The primordials fought the gods long ago, and the gods won, killing several of them and imprisoning others within the Chaos. While no one precisely knows why the gods died, it stands to reason that the primordials will return, breaking free of their chains and returning to their thrones to rule again. This is likely the reason why classes with primal powers – barbarians, shamans, etc – have begun to emerge as the leaders of the world. But the truth is, in the thousand or so years since the gods died, there has been little movement from the primordials. Regardless, the Chaos has remained unchanged, still churning with the elemental power that created the world.
Sigil, the City of Doors – Sigil, too, has remained largely unchanged, save for the changes felt in Khalin – no more divine classes, no more gods. But there is no better place to find a portal to the Astral Sea or the Feywild. Strangely, since the death of the gods, the Lady of Pain, Sigil’s near-omnipotent guardian, has not been seen as often as usual, and the Dabus, the creatures which repair the city, have also diminished. The chant across the ring is that since the Lady has no gods to defend the city against, she has become weakened, and thus does not spend time patrolling the streets as she once did. This has, naturally, led to a rise in crime among the streets, as well as a few Lady-worshiping cults (who are probably worshiping her just because they can).
Far Realm – Legends among the elite wizard guilds of Bapherem said that powerful aberrant creatures from the largely unknown Far Realm infiltrated the Astral Sea and killed off the gods, in a war that lasted a blink of an eye of our time. Whether or not this is true is unknown, as no one has traveled to the Far Realm and returned to speak of it, save for the few who whisper horrible words about it before they die. It is generally assumed, then, that the Far Realm has remained unchanged, though whether that plane has a concept of “unchanged” is also subject to debate.