If you ever come across a situation where you have to do a migration and need to migrate ‘List Workflows’ created in SharePoint Designer, then there is a way!
I found a great article online..
Basically, you have to create a new dummy List workflow without any steps in the new (destination) site, then ‘export to visio’ in both the old (source) site.
Rename both source List Workflow and newly created destination List Workflow vwi files and add a .zip file extension to both of them. Copy the workflow.xoml.wfconfig from the new Workflow zip file to the old Workflow zip file.
Then remove the .zip in the file name and Import from Visio in the destination site.