I made repairing the White Arch Bridge a peace project between all the Thronehold Nations and every Dragonmarked House codified in the Treaty. This gets done in one year, as all of the new inventions and minds honed by war came together to literally rejoin Khorvaire.
Then, I ran a higher level, evil one-shot that takes place on the maiden crossing exactly one year after the signing of the treaty. It was a high stakes train heist that ends with the lightening rail exploding and breaking the bridge again. Oh, also the VIP caboose was filled with the various project managers and mage-engineers that built the thing.
This sets up the normal “good campaign” on 1Zan998YK with the bridge on the map just a broken as normal, but now there’s context why that the players got to take part in as the bad guys that now have made enemies of everyone. I ended up using House Tarkanan as the perps, figure they’re already underground and I can hide their agents (and possibly some of the surviving heist members) where-ever as the aberrant marks can appear on anyone.