Quite clearly, if England and Wales were to be included in the independence referendum. Scotland Yes voters would be in a tiny minority and therefore lose the vote.
I have explained on here before but if we do the sums involved, independence for Scotland could mean permanent Tory rule in England and Wales. Scotland sends 59 MPs to Westminster and at present 58 of them are not Tories. So, at present the Tories would have to get at least 58 MPs in the rest of the UK, before it can even think of winning overall. Without the Scottish buffer, the Tories could run amok and it would be very difficult to get them out of power. Wales also shows no enthusiasm for voting Tory, so you could easily see a situation where English MPs rule over the rest of the UK.
Its in everybody's interest, not least the Scots, that Scotland remain part of the Union.
The pound is another issue altogether. I can't see why they couldn't hold on to the pound, in the same way that the Isle of Man and the Channel Islands do. The pointy heads both side of the border would need to get together to work out exactly how to do it but I can't see why it shouldn't be possible.
All this talk is probably going to be unnecessary anyway, as it looks increasingly unlikely that a YES vote will be forthcoming.