You have no afterlife
Elves in the Forgotten Realms are barred from their afterlife because they betrayed their primary god Corellon by taking set forms, instead of staying flexible shapeshifters like they were intended.
Until he deems it time to forgive them, they are barred from ever entering their afterlive, and instead they reincarnate into new Elven forms after contemplating their failures for a while after death under the guidance of the other Elven gods. This is where the elven 'trance' or 'Remembrance' as they call it comes into play. During a trance, the elf relives events from their own life. But before their adulthood, and after they've reached their elder years, their trances instead allow them to relive their lives in Elven paradise. (Page 36, Mordenkainen's Tome of Foes)
This, of course, creates a strong longing for the Elven paradise, which is where Evermeet comes in. Evermeet is a piece of the Elven heavens that was ripped out of their afterlife by strong elven magic and placed on Faerun. This act nearly destroyed Faerun, and only succeeded because the Elven gods intervened at the last moment to make the ritual succeed.
Evermeet, therefore, is the best next thing you have after actual heaven. Elves who are near death long to go there because it reminds them of a time when their souls were actually allowed into the Elven afterlife. But once they die, their soul is reincarnated into a new Elf.
If you want to truly learn more about Elves, I can recommend Mordenkainen's Tome of Foes. It has a lot of lore about the Elves, their ancient wars and includes the information I've just described in far more detail.
I think the Arcane Age and Karsus's Fall entered canon sometime around 1995-1996.
Karsus was described as a "lesser-known" deity in a half-page article by Eric Boyd published in the February 1995 issue (#104) of the Polyhedron magazine. At this point, Karsus is not a dead power and his demise (from greater deity to demigod) was attributed to his poisoning by a Netherese mage named Wulgreth, who sought to steal immortality from Karsus (ironic, isn't it?). So we can conclude that early 1995, Karsus's story as we know it was not yet canon.
TSR released the Netheril: Empire of Magic (N:EoM) boxed set in November 1996. Yet we can argue that Netheril storyline was already entering the FR canon before N:EoM's publication based on evidence from the sourcebook Faiths and Avatars (F&A), which was published in March of that year. F&A has plenty of information about Mystra that foretells the then-upcoming Arcane Age storyline: Mystryl is given as one of Mystra's aliases; her speciality priests can also be of the CN alignment (Mystrl was CN); one of Mystra's symbols is none other than Mystrl's symbol, a single blue-white star. It is worth noting that one of the authors of F&A was Eric Boyd.
Powers and Pantheons (P&P), a companion to and continuation of F&A, was published in 1997. At this point it is clear that the whole Karsus story is canon: P&P lists Karsus as a dead demigod, describing explicitly the events in the earlier Netheril material; including his 12th level spell, and how he used it to steal Mystrl's power and ended up dead.
1998 saw the expansion of the Arcane Age material further with the publication of Cormanthyr: Empire of Elves. This product is also in full support of the Karsus's Fall story, including all the events in the earlier Arcane Age material.
The conclusion is that Karsus's Fall became canon during the 2e of AD&D.
Best Answer
Paraphrased from the Dragons of Faerun sourcebook:
The dracorage mythal is linked to the appearance of the King-Killer Star. Depending on the position of the comet in the sky, the rage can be localized or global.
In 1373 DR, the link between mythal and comet was broken:
The dracorage mythal still exists, but now the only way to trigger a rage is by using the extremely rare 4th level spell Aggravate Dracorage. This spell only exists in 3.5e though.