Thanks, guys. It is a bit of a mile-stone - or perhaps more of a burnt bridge. Either way, it means it's time to move on.
The funny thing - at least, it always strikes me as funny - is that from this point on I feel no particular attachment to the "old" book. If someone asks the name of it, I struggle to remember. The front of my mind is entirely occupied with the "new" book, even if it's only a few thousand words long.