Scotland sent 59 MPs to Westminster in May 2010, 58 of which were NOT Tory.
I suspect that if Scotland breaks away from the UK, parliamentary boundaries will be redrawn within England and Wales. If not we could be looking at an default win for the Tories at Westminster, at every future Election, except perhaps in situations of a Labour landslide such as happened in 1945 and 1997.
I can't see any reason why a Scottish-born MP in an English or Welsh Westminster constituency would have to give up his or her seat.
But, like Murraymints, I don't think there will be a victory for the Yes campaign, although it is so close that I won't be making any trips down to the Bookies !