There is actually a Wikipedia category on this subject. But more often: There are lots of unfinished books by authors, either because they died before they finished them, or because they never felt what they were writing worked. (In some cases authors have actually published unfinished books, knowing they will not be able to finish them but still wanting to put out what they have finished.) Similarly, there are unpublished books by authors. I suppose the equivalent of a canceled TV series would be an unfinished book series.

It's been a while since I read it, but as I recall he was confident someone would figure out his identity eventually, and then it would bring (what he saw as) unbearable social disgrace on Cosette (and Marius). I also think Valjean's whole perspective was, 'A life with me is forever a life on the run. So I have one mission: Get Cosette to the point where she doesn't have to be with me anymore.' Once that was achieved, I think his whole perspective didn't even really stop to consider, 'Can I stick around?' The idea was, 'She is unburdened of me, now I can disappear.'

The 2012 film had its strengths, but it is not the same experience at all as the Broadway musical. But I'm not suggesting you watch the musical (though, I mean, definitely do if you get the chance), I'm just suggesting you listen to it (specifically, the Original Broadway Cast recording). You already know the story, so you should be able to follow along pretty easily. If you find you enjoy it, then I suggest getting your hands on the filmed 25th Anniversary Les Misérables in Concert, where much of the original cast partially acts out the musical while singing it.

I think you're right that Marius, Cosette, and in fact every character in the book is not meant to be a portrait of an unerring person, just a person, flawed and pitiful. Marius and Cosette are young, immature, selfish, and silly. Marius doesn't know any better way to get close to Cosette, so he does what he does.

As for Jean Valjean's decision to reveal his identity, it is to save an innocent man going to prison for his (Valjean's) crimes. In the musical Valjean expresses this sentiment as, "Can I condemn this man to slavery?" and "If I speak, I am condemned. If I stay silent, I am damned." If you haven't listened to the musical (the Original Broadway Cast recording), absolutely do; obviously it greatly condenses the story and changes a few things, but I think it captures the book actually exceptionally well. I think it will prove a great chaser to the book.