If you've lost all your book source files

If you've lost all your source files and your lulu book has disappeared, making it impossible to download PDF or doc, you can buy your epub from any site, download that, merge all parts in Sigil, copy, paste in Word doc and start reformatting. You'll have the images (whose resolution you can increase in Photoshop) and the edited text. It's a start.

You can also look in your emails, drop box, Google Drive or even pirated versions of your book. Pray someone liked it enough to try and share it.

Good luck.