The ebb and flow, ups and downs, of DGN is such a steady phenomenon, it could seriously be an academic subject. It's like the stock market.
Some DO disappear for "forever". I do wonder where these people go to, or where their lives are taking them, and why they never came back. But I was used to this easy come, easy go, notion of people from hanging out in Royal Oak back in high school...trust me, there was a way higher turnover rate.