I’m guessing you didn’t read the novel (can’t say I blame you, the writing quality of magic novels was inconsistent at best.) The plot ended with Lorwywn-Shadowmoor’s day/night cycle returning to its natural cadence. Rather than mirror planes that transform every 1,000 years or whatever it was, they’re just the daytime and nighttime states of the same plane now,
Obviously they could retcon that, if they think doing so would make for a more compelling story for the return set. But that was the state of things last we heard.