We don't have any other case studies that deal with this migration specifically, but there are people hanging around here who have moved from celery.
We are doing a lot of work that should help this type of transition even easier. I know that our product team (@justabill) would possibly be interested in talking to you about your use case.
While I don't think he did a 1-1 migration from celery to prefect, I'm also tagging @Abhishek here, who has worked with both tools in the past.