Algo así tal vez funcione:
use MuOnline
delete from CashShopData where AccountID in (select Id from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null)
delete from CashShopInventory where AccountID in (select Id from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null)
delete from MEMB_INFO where memb___id in (select Id from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null)
delete from MEMB_INFO where memb___id not in (select Id from AccountCharacter)
delete from MEMB_STAT where memb___id in (select Id from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null)
delete from ExtWarehouse where AccountID in (select Id from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null)
delete from warehouse where AccountID in (select Id from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null)
delete from AccountCharacter where GameID1 is null and GameID2 is null and GameID3 is null and GameID4 is null and GameID5 is null
En teoría eso elimina de las tablas correspondientes:
-CashShopData = Tabla de WCoin
-CashShopInventory = Tabla de Inventario de Wcoin
-MEMB_INFO = Tabla con la información de las cuentas
-MEMB_STAT = Tabla donde se almacena la información del estado de la cuenta y última conexión/desconexión
-ExtWarehouse = Tabla con la información del baúl expandido
-warehouse = Tabla del baúl
-AccountCharacter = Tabla donde figuran los slots de cada personaje (si es null, es porque ese slot no tiene personaje y si los 5 slots son null, entonces la cuenta está vacía).
Faltaría hacer un check para MEMB_CREDITS pero me tiró un error de conversión y me dio paja acomodarlo. Probalo así, eso seguramente funcione bien y elimine las cuentas vacías sin importar si fueron recién creadas o hace mucho.