What does it mean, you cannot edit? Is it a site workflow or a list workflow? If you click on it, what happens? In a nutshell, create the user again in AD with the same login, set up password - open browser in "anonymous mode" or use "open as a different user" - fill in login and password and try to edit the workflow. Check for the permissions.
It may happen you cannot edit workflow cause of insufficient permission.
Tell us more.

Steo

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What it means is that once a user who created or modified a workflow is no longer in AD the workflow then errors out as it cannot verified the created/modified by user. This is true for list/libray workflows as well as site workflows. Our agency (federal agency) does not create system accounts nor reinstate AD accounts once a person is no longer with us. We found a way to again open the workflow and through export and import steps create a new one publish it That meant create the new one with a different name then delete the current one. We would need to constantly be doing this anytime a person who created/modified a workflow is gone. Not an elegant solution but worked.

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