The way archival works is by publishing the process in an archived state. Hence, since it’s a publication of a process, it follows the same approval rules as when you would normally publish your process and would trigger the same notifications based on how you have set-up your Process Group e.g. Process Owner/Expert, Informed stakeholders etc. Hope that makes sense. 

Most of the processes that get archived are only in their “in-progress” state and not published. For example, a user creates a new process and realises that it is wrong and want to archive the process. If the process expert or process owner doesn’t approve the archival request then the process just sits there and clutters up the process list in that group. I was hoping that a promaster could be notified so that they could archive the process on behalf of the process owner or expert.

I see. What you are describing is already happening. The Promasters should be able to see all those notifications for “Pending Archive Approval” under their Dashboard > Changes. They can additionally further filter by selecting the “Processes for Approval”. Where regular approvers would have the option of Approve/Decline only, the Promaster has an additional option to “Archive Now”, bypassing the approval mechanism.

If your Promaster does not see that option or the notifications are not coming through, then I would raise it with support@nintex.com with some specific examples for further investigation.