If the task is assigned in process model and it is still in pending and it arrives archiving time then the process will be archived or not
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for example : if we give archival as 3 days for any process model, once process is completed or cancelled that process instance will be removed from system & It will keep in backend side memory.
for example : if we give deletion as 3 days for any process model, once process is completed or cancelled that process instance will be removed from system & It will not be stored in the back end.
if we use archival we can restore archived process instance using unarchive command in backend side or else we can raise a ticket with Appian they can help us to get back archived process instance