Thanks a lot, the picture starts to become clearer. So just to summarize some of the possible circumstances in a timeline-like fashion (only as an interpretation ( one possibility):
Before his death, Broyan managed to purify at least the Orlanth temple in Whitewall, eventhough the city now is basicaly a haunted ruin, with only the Stormvoice and probably some Stormbulls and Humakti being able to find a safe passage through the chaos-tainted ruins to the temple.
A season or so before the Dragonrise in 1625, Broyan and his troops made camp outside Twotop, close to Auroch Hills and the Troll Woods.
It is not unlikely that he was preparing to march on the new Lunar Temple.
Somehow some deadly entities (perhaps a Black Eater, Darkness elementals and / or Hell demons and maybe more) surprisingly manifest in the camp one night, slay Broyan and massacre lots of his troops in their sleep, not unlikely summoned by foul Lunar sorcery (maybe even in combination with intruders, assassins or someone preparing/helping the summoning, maybe even a traitor and/ or other allies?).
Broyans powers likely failed him because of a broken vow.
He is layed to rest in the cairns of his kin, leaving no heirs. Vingkots Sword & Helm are likely lost for now.
The survivors dont really know what exactly hit them, probably starting to blame each other and split up due to internal conflicts and rivalries. Rumors about the incident spread.
Part of the survivors settle in Newtown, in front of Whitewall ruins, forming the new Olontongi tribe, another group with Leika Blackspear is probably off to Sartar (Colymar lands?). (Kallyr Starbrow is off about to start her rites provoking the Dragonrise.)
Heortland is now facing a power vacuum, endangered and destabilized through internal conflicts, the Shadowplateau trolls and the Scorpion Queen.
Since the real responsibilities for the murder of the High King are not really known so far, revenge for him isnt too likely soon (eventhough there is a chance, some of the involved powers fall victim to the Dragonrise).
Lots of work for Heroes