Not sure how your backend works, but I read a neat technique by I think Second Life, where each actor is in a zone, and a zone is managed by a server.
If a player leaves the zone, their entire code stack and current state is shipped to the next zone (script hand off) without the player noticing. They mentioned because each actor is running in a VM/scripting language, the servers can pause/resume the VM for that actor on any machine they move to - pretty neat.
The Second Life approach sounds like a very good solution if you're having to, and willing to use multiple servers because of performance reasons. I think Angeldust's architecture is a bit cleaner and more straightforward due to different design goals. I specifically wanted to reduce complexity and keep a simple infrastructure so that I could code, debug and manage everything on my own.
I also have the luxury of using a single, big, many-core server if necessary. When Second Life started I don't think 32+-core servers were a thing, so their scaling model was probably also born out of sheer necessity.
If a player leaves the zone, their entire code stack and current state is shipped to the next zone (script hand off) without the player noticing. They mentioned because each actor is running in a VM/scripting language, the servers can pause/resume the VM for that actor on any machine they move to - pretty neat.