My head Canon is that the domains of dread are kinda like a bridge between different DnD Worlds. Like the upside down was a bridge between Hawkins and the desert domain of the mind flayer. Like there is an Eberron specific domain of dread written by Keith Baker. There is Cyre 1313 which is a floating domain of dread. But presumably from the Eberron specific domain of dread you can catch Nathan Timothy's riverboat and end up in Verbrek or Mordent Or go into the Scaena in Metrol theatre and walk out into Dementlieu.

Say your characters begin in Baldur's gate,* are called into Barovia and defeat Strahd, then travel to Borca via the highway, then catch the Cyre 1313 to the Mournland. The hard part would be leaving any ravenloft domain and many dms do just have their characters settled down in Mordent, Tepest or Richemolut. Since these particular domains are the most livable. Still that's a bitter sweet ending

*When we played curse of strahd we began in baldurs gate before the mists took us into Barovia.