To clarify: Scribus does not save the images in the document, it only saves the path to them. If you move an image, or move the document, the path will no longer be correct and the image will not show.
If you want to "keep" the document it is usually suggested to do a "Collect for output". This will save the document, and copies of all images it is using, into the same folder.
Note copies, this means using Collect for output will created duplicates of the image files for each document.