Whether it will be a cohesive whole at the end is debateable - we will just have to wait and see (and bury our heads in the sand if it's not!) :)

At the moment I'm just going with the "write a scene if it appeals" approach - I've never had a whole plot fall into place so easily and I'm loath to do anything that stops the creative juices flowing. If that means writing the end before the beginning ... well, I'll just keep my fingers crossed that it works out.