I have been migrating a list with ShareGate. The list's workflows were modified on the destination, but for the sake of quickness I deleted the list before I re-migrated it.
The workflow for the list remained intact; however, there was no way to associate the list with the workflow, or to associate the workflow with the list. The workflow is now freestanding; it refuses to associate with a new list because it wasn't designed as a re-usable workflow.
I've seen suggestions on using Visio 2013 Premium to convert the workflow between types, but I don't have that program right now.