Hello!
My understanding is that unless you schedule a Purge job it will be gone once you have fired it.
However, I have not tried this but there will be an entry of the Purge in in the queue (wt.router.5.2 if I remember correctly) in case Windchill is set to store completed queue entries. It may be possible to set the status to ready to trigger the job again.
Cheers!
/Peter