The system will evict the live object when it has been idle for some period. If there are connections still open to the object, it won't be evicted (unless it exceeds resource limits, etc.).

As always, "cold starts" with Workers are very fast, usually imperceptible to a human. Also, multiple objects may be hosted in the same isolate; when instantiating in an existing isolate, the only "cold start" overhead is whatever you write in your class constructor.

> Can objects contain relationships that are themselves references to other Durable Objects?

Yes, by storing the object IDs.