Things don't always work out the way they are planned or discussed. Last summer (2010), my boss and I were discussing the end of my assignment at year end 2012...with him essentially asking me to stay, me saying no, then both of us agreeing that I would stay with the company but spend a couple weeks in Asia per month and do everything else remotely. That led to a discussion this past summer (2011) with me again being asked to stay...and me actually ready to accept it, with a caveat that I take home leave more often.
I did take the step, however, of getting the boss to agree to promote my intended successor to an interim step. It was hard for me to do...Kind of like walking our daughter down the aisle (I do know that feeling, as I just did it in August).
All in all, I'm relieved that we are taking that step, but also relieved that I can oversee the transition of power. I've been here so long, and have grown the company from what it was when I inherited it to 3x the size, and watched it shrink again during the recession...but all the while maintaining a respectable profitability that my predecessor could never achieve. Now it is time for my successor to take the controls and grow it again, to level I did not or could not achieve...and since it is my baby, I'll be smiling when he does.
Moral of the story...be flexible. Be in tune with your bosses. If they are good people, good leaders, and are able to coordinate a smooth transition with you, then maybe indicating your goals early is a good idea. If your boss is just another SOB you have to work with for another 6-9 months, then maybe it's best to just give the minimum notice required by company policy to get your retirement/bonus/options/restricted stock, etc.
FWIW
R