Combining all chapters into single story

I have 50 chapters in a story which I’m editing in Scrib. I want to collapse them into one file (not for export). How do I do this?

If what you want is getting a single file out of your 50, then choose all the files you need in the binder, then choose Documents > Merge.
The operation IS NOT undo-able. Try on mock files first, or copies, and just choose a few of them to see the result. It might take a few seconds to complete.