It's bad for business to delete unused accounts since big patches and expansions always bring people back. If those people find their level 50 (or whatever) gone, they'll be a might upset. As an example, a few months ago I reloaded EQ1 (out of nostalgia) after not playing it for 10 years and all my characters were still there. Can't speak for SE directly, but MMOs in general do try to keep characters around.