Some additional discussion re: finishing the first draft, from my LibraryThing discussion thread:
(WARNING: possible mild spoilers (by some definitions)):
"As to whether the story worked out as expected - it depends on the time scale. The book I ended up with is a good bit different from what I expected when I started it a year ago, not so different from what I expected a few months ago. Part of the difference is due to my finding a good bit more Roman-related history in the time frame and area I'd chosen than I expected. To simplify extremely, I started with the idea "hero is born, grows up, goes to another country, has many adventures" and ended with "hero is born, grows up, goes to another country". The "many adventures" part, it seems, will eventually require another book...
"I haven't ended with any major loose ends, although I think I'll find a few places which need a little more explanation, but that's OK because although my word count is currently very close to my estimate (103,870 at the moment, with up to 1,000 more to go, vs. an original guess 6 months or so ago of 100,000) the page count is still comfortably below my maximum. On the other hand, there were certainly some bits I didn't expect along the way - as you say, characters (if they're good, well developed ones) frequently have a will of their own. This is one reason I don't write to a detailed outline - I find it more fun this way!
"The afterword, by the way, explains which characters and places are invented (almost all and only a couple, respectively), and includes most of my blog comment re: lack of information on druids in general and British and Irish ones in particular. I wouldn't want anyone to confuse any of my invented druidry with established fact, although from what I've heard about other writers' experiences, it's likely to happen anyway."