In this timeline, the events of The Verdant Passage go as written up until the final fight. Kalak tries his accelerated metamorphosis spell, Rikus wounds him with the Heartwood Spear, Kalak retreats into the ziggurat and the heroes pursue him.
But that last fight against the wounded, metamorphosing Kalak goes differently. Perhaps, knowing he’s dying, Kalak unleashed some devastating final spell out of spite? All that is clearly known is that a few minutes after Kalak was wounded by the Spear, the ziggurat collapsed completely, burying the sorcerer-king and his foes under thousands of tons of rubble. The templarate suddenly loses spell abilities.
Tyr is free of Kalak, but there is no Tithian to claim the throne, no Agis to rally the nobility.
Probably, without PC intervention, the templars are nearly all killed very soon, either by angry mobs or by the nobility. With the templars losing their spells, and no sorcerer-king to back them up, and no Heroes of Tyr, the nobility is the only meaningful power bloc left. They will probably act quickly to consolidate that power, killing or enslaving any templars the mobs haven’t already gotten to.
The Senate is the only remaining governmental body of Tyr, and it’s used to being essentially powerless. But something is needed - Tyr is vulnerable to its enemies now. If Tyr is to remain free of a sorcerer-king’s rule, someone has to lead its defense.
And two artifacts - the Heartwood Spear and Ktandeo’s Cane - are still buried under all that rubble… And there’s a halfling chief out there who will be expecting them back…
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This leaves a free city for PCs, but there are no Heroes of Tyr around to overshadow the PCs. The PCs can lead the protection of Tyr from Urik, etc.