It does seem that you might try re-arranging your work flow. I have been through several iterations.
> It's not necessary to embed all images in Scribus files in order to embed them in the PDF. It just makes the .sla file
huge. I think that .svg images do have to be embedded. But if .png, they don't, and they still will embed themselves in the PDF file, which will be just as huge as ever with those 600 DPI images.
> I have learned to keep each Chapter in its own scribus file so that the files are smaller, not overloaded with images,
and Scribus does not cludge down as it did with larger files.
> I also export every chapter to an individual PDF file, and I can deal with these 12 or 15 smaller PDF files a lot easier
than one big one. _Anybody_ can then assemble them in order with a PDF tool. Note that you have to go to the setup and set the page numbers for each chapter individually before you go to PDF.
> Having a whole lot of images scattered around the hard drive is a royal nuisance if you want to edit one. IMO it is much better to copy each image to a "graphics" sub-folder under the one the .sla file is in, so that you can find the file when you want to. If you have to go back to a GIMP (or, Illustrator, Photoshop, Inkscape, etc.) file to edit one, then when you are first collecting the pics into your subfolder, just put another subfolder where you can put the associated Gimp files as well, so they are handy.
> the "Collect for Output" function is a piece of gold, it really works well for collecting all those graphics files that you have already got scattered around. Check it out. The only thing it won't do is bring your GIMP or INKSCAPE source files along.
> Here is a proposed course of action to consider: Take that giant file, when you get it repaired, and immediately do "save as" a dozen times or so as necessary as Chap_1, Chap_2, etc. Then, open each file individually and chop out everything else except one chapter (careful). Then, do "Collect for Output" to a completely new folder structure. Each Chapter needs its own folder for "Collect to Output", so set these up first. The .sla file and all of its associated graphics will be dumped together into a folder. Note that you cannot cut and paste the .sla file anywhere else, because it will break the internal links, but what you can do, if you want all of the .sla chapter files to be in the folder above where all the folders with the graphics are, then you have to do a save-as individually for each one, and then you can delete the .sla file that is in the folder with all the images.
Make a separate folder called PDF_output, and put all of your exported PDFs in there, where they can be assembled, or zipped, or whatever. When it comes time to send this all to your printer, if you have to do that online, it will be a lot easier to transfer the smaller PDFs. If your POD company is sympathetic, they will assemble the PDFs, but in fact that seems unlikely. But check it out. Hope your get your files fixed.
jack