The life of an 'instance' in ED (as I understand it):
When you log on to the main menu, you are connected to a matchmaking server, when you choose Open, Group or Solo to enter the game the matchmaking server will try to put you in an existing instance hosted by another player if possible, subject to the mode (open/group/solo). If you choose solo of course no match will ever be found, it will always create a new instance, as it will in the other modes if no suitable instance is found.
Let's say there are two players in an instance. One arrives first, no-one else is already there so a new instance is created, the first player is obviously hosting it.
Second player arrives, and joins the instance hosted by the first.
First player leaves the instance, second player's PC takes over that instance and control of any NPCs etc, the instance remains until there are no players left, then the instance is destroyed.
So it is possible to wait for your CLogging 'friend' to log back in, using the same choice (open/group) as before, and they will re-appear in your instance. CMDR_Cosmicspacehead's idea in
Post #34 works by only allowing the CLogger to rejoin the game in the same instance they left behind (assuming it is still there).