No, it is not as clear as that, I'm afraid. I think what would happen is that the MPs in the Commons who represent Scottish constituencies would be out of work, irrespective of where they were born. Most were born in Scotland but that is not the point. On the hand, Scottish-born MPs currently in the Commons but representing English constituencies would continue to represent those same constituencies in the Commons. Place of birth is not the deciding factor here. We have had, for example, German-born MPs in the Commons. But what will happen in the future?
Sitting MPs, particularly long-standing ones who have been "good" local MPs in English constituencies, may well continue to be re-elected by their constituents; Scottish independence would not much change that.
For the future, Scots-born aspirant polticians would have to decide whether or not to try to become an MSP in Holyrood or an MP in the House of Commons. If the latter, they would be in the same position as all other prospective MPs. They would have to be selected as candidates by their local party members and, come the next election in that constituency, be elected (or not) by the local voters. The unknown factor is whether English voters will wish to be represented by a Scot in the Commons? On the whole, English local political party members and voters in English constituencies have been more open to electing someone who is not English to represent them than has been true in Scotland.
By the way, that is not a sleight on the Scots (I have lived and worked there for many years in the past, have family though marriage in Scotland, all my children were born there and have many Scots friends) but a statement of fact, based on the past record. I am aware that part of the reason for this is that, by and large, English politicians would not consider a career in Scottish politics, whereas the opposite is clearly not so.
I lived in Scotland in the late 1970s when there was a referendum on Scottish devolution and, though English-born, got a vote. There was a a slight majority in favour of devolution but the turnout was less than two-thirds of the electorate. One of the rules was that at least 40% of the whole electorate had to vote for devolution. As I recall, this rule was introduced as the result of an amendment to the devolution legislation tabled by a Scots-born MP representing a North London constituency (Edmonton?). Anyway, the vote and the turnout meant that only one-third of the electorate had supported devolution and thus it failed at that time. As it happens, my view is that a simple majority (50% + 1) should not be sufficient for any such constitutional change. I would apply this not only to a referendum in Scotland but also to any referendum on, for example, change within the EU. These are issues that are so important that a substantial majority should be required.
