For those who don't know, the reason it was left unfinished was because of a case of what TV Tropes refers to ironically as Author Existence Failure (ironically because the name of said trope is based on a line from one of Adams' own books, Life, the Universe, and Everything with reference to the fate of the Starship Titanic) - Adams' sad death in May 2001.
And now I've finished reading it - the novel bit itself, that is - and loved it, I kind of want to know what happens next. But I can't, obviously. Part of me is tempted to go to ao3 or fanfic.net and see if there is any Salmon of Doubt fic. I presume there is, fans have had 12 years to come up with the stuff - but no fanfic can really do justice to Adams' work, can it? Or can it?
If you hear me whimpering, I've succumbed to temptation and been massively, massively disappointed by what I've found...