Tough to say. I've been on forums for over 20 years (only the last 9 or so on political forums) and have lost members to fatal accidents, one to prison for murdering his mother (he was a LW nutjob!), a few to cancer or other unspecified illnesses. Some are just banned and find a nicer place to visit.
FWIW, I never understood why people who are banned keep coming back for more. It's a bit "off", to put it nicely. Masochistic at best, possibly Bipolar at worst. Thoughts, anyone? Why would a person who is banned from one forum change names and come back for more?