Mommooshka As Gaiman said in his Newbery Medal acceptance speech for this book, he realized as he was writing the ending "I was now writing about being a parent, and the fundamental most comical tragedy of parenthood: that if you do your job properly, if you, as a parent, raise your children well, they won't need you anymore. If you did it properly, they go away. And they have lives and they have families and they have futures."
This answer contains spoilers… (view spoiler)[I know this is a 4 years ago question, but my take is a little different. I thought the residents of the graveyard promised to keep Bod safe and, with that promise, gave him freedom of the graveyard. Once the threat to his life had ceased to exist, that protection and all it encompassed, was no longer needed. (hide spoiler)]
K. D. Also, I wouldn't worry too much about Bod being able to take care of himself in the world beyond the graveyard. By the end of the book, he has shown us that he is a resourceful young man. I have the feeling that this might not be the last time we will read about Bod Owens.