Before January 20, 2011, single characters were deleted automatically if they had not been used ingame for a period of months which equalled their level (e.g a character with level 20 was deleted after 20 months). This rule applied to all characters on accounts without Premium Status, even if the account had been Premium a short while ago.
Further, characters on accounts without Premium status were deleted regardless of their level if they had not logged into the game for 720 days.
If an account contained no characters anymore, it was deleted shortly after.