Back in '07 I completed NaNo and reached an ending. But once I began editing phase (which for me actually begins in January) I realized the beastie really didn't work. So through '08 I added a bit, tossed aside a bit and by November realized I had to do it again! I also discovered that one of my characters had managed to get herself pregnant along the way. Serves me right for letting her run off on her own!
50 K words later and with a successful NaNo '08 under my belt (so to speak) I had my main characters strewn out across the country and generally had no idea what to do next.
And through '09 I tried to settle and finish it, but every time I thought I had a hook in the beast something unexpected would happen.
And so November arrived....
By that time I knew more or less where things headed (or so I believed) and even spent a good bit of the first day or so working on my time line (a thingee that some people might call an outline).
I tossed a section where a character went into the mountains and and managed to get himself caught in a blizzard (never a good thing) and rerouted him north (things are warmer in the north -- think southern hemisphere). I even managed to rescue a character from having to cross a swamp full of undefined nasties! If I had known more about August in the Louisiana bayou, I might have let them go! Could have been fun.
And things moved along as they always do.
Then about three weeks into NaNO '09 my rerouted character decided he had to go somewhere and the dweeb wandered back into the mountains! Another character went off without his protector and a third decided to do something good by conning every body (an idea which seemed about as bad as any I had managed to come up with).
And all this about 6 or 7 days before I had to wrap this thing up!
Well, somehow it all worked out. A few people paid for their foolishness, more didn't and everybody lived happily ever after -- well, OK, not really, but I did manage to pull a few things together and get to a semblence of an ending.
So, what's my point?
Just this, that if you want to do NaNo or some such enterprise (there's a group who plan to write 5,000 line Epic Poems in May: NEPMo.com, if you're interested) and your characters just won't cooperate then just write what they happen to do at the time. Describing the weather and what a character happens to see off in the distance can buy a few words as well....
Eventually, your character's will drift around to getting where and doing what they ought. Trust the little creeps, they most likely know what they're about better than you do.
And just keep writing....