This is a great list and I would love to see a serious of fanon adventures each exploring one of these ideas.
I would suggest that there is little chance of an island wide cataclysm.
1) The Jarin are on the cusp of starting a second rebellion in Orbaal.
2) King Minigath is about to expire without an heir sparking a Kaldoric civil war.
3) The Earl of Tormau and King Chafin III are about to start a Rethemi civil war.
4) Kronas Elernin plans on attacking either a) Kanday or b) the Tulwyn so that he can declare himself emperor sparking a Thardan civil war.
5) Gwadira, a Lothrim-like-figure, is about to lead the gargun into a takeover of Harn.
6) A sect of the Church of Naveh is taking over the equally vicious Pagaelin to attack everybody in reach.
7) The Lady of Paladins are leading a 'crusade' against the Solari which incidently ticks off, in no particular order, the Council of Eleven, several major Melderyni nobility, the Laranian Church, and the Kaldoran fighting order.
8 ) Certain Hodiri tribes are contemplating taking over Chybisa.
9) Chybisa could shortly be in a succession crisis.
10) The Obodu and Iorzu, the largest Kuboran tribes, are about to fight over who leads the tribes for the invasion of Rethem.
11) The Agrikan fighting orders want to lead a crusade against a) the Kubora and then b) the rest of Harn.
12) The Urdu vs. the Equani vs. the Ymodi are in escalating conflicts.
13) The Morgathian Church wants to take over Harn.
14) And of course, Gwydriel and the dark elves are up to no good....
An alternate view:
Future Happy Scenarios
1. The Jarinese resistance fails to coalesce. Orbaalese successfully defeat the fragmented pockets of resistance.
2. King Miginath soldiers on, defying all expectations of his imminent death. The Kaldoric Succession Crisis is postponed for years.
3. Chafin III's agents successfully assassinate the Earl of Tormau and his niece and nephew. Royal forces, supported by the Roving Doom, Warriors of Mameka, Red Shadows of Herpa and the Earl of Ithiko easily retake Ithius before moving on to Tormau and quickly dispersing Tormau's army (left leaderless and unpaid by Tormau's death). The Earldom of Tormau is awarded to a Chafin III loyalist.
4. The Imperial Faction of the Thardic Senate forms a coalition with several other factions. Kronas is peacefully elected emperor. He decides to spend the next five years consolidating Tharda's position (a condition of earning the support of the Consolidation Faction) and expanding and improving the legions. He also retakes Themeson before negotiating a peace treaty with Chafin III.
5. One night, while walking among here gargun subjects, Gwadira is unexpectedly stabbed in the back by an insane gargun. A civil war breaks out and her hidden alliance is shattered with her death.
6. An "unknown group of adventurers" lead a raid on the Navehan Temple in Bejist, fatally weakening the Navehan Church.
7. Support for the Solari Crusade collapses. The Lady of Paladins in Kaldor split from their parent order causing a crisis in the leadership. Under intense presure from the King of Melderyn, the Laranian Primate relieves the Grandmaster and orders an end to the crusade.
8. The Hodiri fail to come together under a single chief. Chybisa suffers repeated attacks, but only from one or two trbes at a time. There is much damage to their western manors, but the kingdom survives...for now.
9. The heir-apparent, Prince Balesir, goes completely crazy from syphillis. King Verlid VII names Princess Nerelin his daughter, as heir-apparent and her husband as Prince-Consort. There is much relief when the Princess gives birth to a healthy son.
10. With the defeat of the Earl of Rethem, Rethem is in a much stronger position. Kuboran warriors fleeing the King's attack on Tormau bring word that Chafin III has unified Rethem and is ready and able to fight off a Kuboran attack.
11. With his victory over the Earl of Tormau and the peace treaty with Tharda after the fall of Themeson, Chafin III has solidified his control of Rethem. The next to fall is the Copper Hook. The Royal forces, supported by the other three fighting order, decend on Hyen. The Copper Hook is crushed in an overwhelming attack. As a reward for their loyalty, Chafin III awards the keep to the Roving Doom. In return, the Roving Doom return Teregan and its subordinate manors to the crown. Chafin III combines them with the Agrikan Primate's estate at Vinarsa and gives permission for the Primate to build a keep at Teregan.
Faced with a suddenly unified Rethem and Tharda under a militant Emperor, Kanday faces a crisis. Under intense pressure, King Andasin IV marries the daughter of the King of Melderyn (if I remember correctly, he has one available, I don't have my books with me). Kanday and Melderyn sign a military treaty. Having successfully terminated the Solori Crusade and installed a new, more biddable Grandmaster, King Chunel orders a large contingent of the Lady of Paladins to Kanday to reinforce the northern frontier. King Chunel sends embassies to Kronas and Chafin III to make it clear that any attack on Kanday will be considered an attack on Melderyn.
12. War breaks out among the Urdu, Equani and Ymodi. In the civilized kingdoms, no one notices.
13. King Chafin III, well supported by the fighting orders of the Agrikan Church is now sufficiently secure to constrain the Morgathian Church and bend them to his will.
14. Gwydriel and the dark elves get tired of the "mayflies" and hop the next boat to the Blessed Realm.
You see, it is all in whether you look at the glass as half empty or half full.
So, depending on what you want from Harn, simply choose one scenario from the "Future Bloody Scenario" and the rest from the "Future Happy Scenarios" and you can take Harn in what ever direction suits your preferences.