No one is writing stand-alone novels any more. Go stroll through Amazon’s ebooks, and you’ll see that virtually everything you see is “book one in the Fartknocker series.”
Now obviously, that’s not true, and probably never will be. People will always write stand-alone stories with no sequels or long-range plans, and publishers will more than likely always buy them–but lord, don’t they love them a series.
That’s where it comes from, you know. People see publishers putting all their marketing and effort into this or that series, and assume–almost certainly incorrectly–that they are only interested in the next big series. Therefore, everything has to be stretched into a series, whether or not it has the potential for it. So, sadly, many great characters and stories are forced to keep shuffling across the stage long after they should have been allowed to take a bow and fade into the background for the next act.
I’m about to propose something radical. I preface this by saying that I do, in fact, have a moderately successful series of my own, although my favorite of my works remains a single, stand-alone novel. But I think this merits saying.
FORGET ABOUT THE SEQUELS AND WRITE THE BOOK.
Don’t worry about it. If the story doesn’t merit a return, then don’t go back. Finish the story, and let it shine on its own. If it has the potential to be a series, it’ll let you know. Don’t force it.
After all, imagine how lame a sequel to Dracula would have been. (Actually, you don’t have to imagine–there are countless lame novels vaguely based on what happened after the good Count lost his head.)
Tell the story. If it’s done, it’s done; don’t try to reanimate a dead story line to stretch it out.