yes oracle will create a new one.
cd $ORACLE_BASE/admin/SID/bdump

SQL> !cp alert_SID.log old_alert_SID.log

SQL> !rm alert_SID.log

SQL> execute sys.dbms_system.ksdwrt(2,to_char(sysdate)|| ' I have just create a new file.');


PL/SQL procedure successfully completed.

SQL> !cat alert_SID.log
Fri Jun 20 17:08:37 2003
20-JUN-03 I have just create a new file.