After a Workflow is completed, it gets automatically archived. Here's how to see archived Workflows, and unarchive them if you wish to.
1. Show Archived Workflows
From the Templates page, under the "Show workflows that are.." click "Archived" switch:
2. Search for the Workflow's name
In the search field, start typing the name of the Workflow. It should appear below. Then click the template to view its workflows:
3. Un-archive the Workflow
Click the menu icon on the right side of the Workflow you want to unarchive:
Finally, click the "Unarchive" menu item:
You will see a promt that you "Unarchived Successfully" the template and you can now open the workflow.