I have thought this too, although not in such detail as you obviously have. If you remember in Asimov's Foundation series, one of the books, third?, this question was bought up and the reply was that Daneel - or whoever it was being talked about - was a highly developed robot, and if ordered to end his own existence he would question the order. If he fully understood the reason for it being necessary to end his existence, he would do it, but otherwise he would be asking for confirmation from.., somewhere. Can't remember enough of it and it is about ten years since I read the series.

Bad time to give me a hunger for the series again too - I have two assignments due soon.