When a chat room owner is deactivated, the next user who has been in the room the longest automatically becomes the new owner.
For example, a chat room contains three users: User A, User B, and User C. User A is the owner, User B joined a day after its creation, and User C joined a week later.
When User A is deactivated, User B becomes the new owner and a system message will be posted to notify all other users, User C, that the owner has changed.
Note: If the deactivated chat room owner is reactivated, they will not automatically returned to being the chat room owner. This functionality is by design and there is no setting to amend this.