I have a big document that was rearranged so that the chapters are now "mixed", meaning that they were single "blocks" before, and now it's a few pages of chapter 1, then a few of chapter 2, then 3 and then 1 again and so on. The initial chapter blocks had linked text frames with running footnotes. The text frames would need to be mixed in the same way, but the footnotes still need to run continuously.
Unlinking the text frames leaves the text still belonging to the initial frame, and adding frames to the row doesn't work either.
And if this wasn't enough trouble: each chapter has its paragraph style that needs to be maintained.