Anon, I would not be too harsh to blame him or other siblings for leaving school early. He is not the first and certainly not the last kid who decided that playing ball in college is not for him/her. Some kids do find it difficult to live away from home, some others can't handle the demands (school, training, games, travel). Sam has a great potential, far greater than Harry's IMO and good luck to him whatever he decides to do.
And it will not hurt his Draft options, he may just need to figure out how to create a greater exposure. The Draft is all about potential and not so much about attitude.