BEGIN
    FOR i IN (SELECT t.username
              FROM   dba_users t
              WHERE  t.username LIKE 'abc%'
                     AND t.username NOT LIKE 'abc_this_one_save') LOOP
        EXECUTE IMMEDIATE 'DROP USER '|| i.username|| ' CASCADE';
    END LOOP;
EXCEPTION
    WHEN OTHERS THEN
      dbms_output.Put_line(SQLERRM);
END; 

SELECT t.username
    FROM DBA_USERS t
    WHERE t.username LIKE 'abc%'
    order BY username;

when others

SQL Error [1940] [42000]: ORA-01940: cannot drop a user that is currently connected
ORA-06512: at line 13
ORA-06512: at line 13