For me, over the years a lot of friends have come and gone online and I haven't always known what became of them (they just "disappeared"). I think for those that are really good online friends, they are in multiple "places" with me online so I'd probably learn somewhere; I have people change boards or stay on boards I don't anymore, etc. and others that end up only being occasionally email buddies for jokes, we don't see one another on boards anymore at all. But it takes time to become a good enough friend and I don't think I'd feel it was something I "did" if a good friend disappeared and I didn't have a way to find out what happened; I would probably assume they had died, based on past behavior, versus that they had just "left" me.