Copying and pasting from a PDF to the Code View, is not too terribly difficult, IMHO. First, the PDF displayed the format I was aiming for. But I had prepared for the transition by making several images for things like the unusual fonts I'd used for the title and subtitle/author name, the graphics used to set off the title and that were used between the "Chapter X" text and the chapter title, etc.
Secondly, while iBook Author is very good, especially for anyone who has used Pages, it is made to output an ePub in a specific 'bundle' mainly for the Apple Store/Reader. (and Calibre didn't like the wrapper, so it wasn't suitable for other formats). Like Sigil, it doesn't save the raw data for transferring that to another 'authoring' app. And you don't even get to see that raw data the way Sigil allows in Code View.
While BBEdit truly is a better text editor, I haven't even investigated trying to display the source code in its built-in 'browser.' And I doubt it would too accurate. But I must also admit that I have not even looked at the Sigil 'preview' section, either! Frankly, I was too wrapped up in just getting the 90+ pages entered!
And correcting the copied paragraphs was pretty simple, since I had the PDF viewer open. It was mainly a matter of pasting in the "</p>\r<p>
" in at the end of one paragraph and the beginning of the next. Somewhat tedious, but not mind blowing. Of course, at my age, I might not notice too many brain 'explosions!'