They would have to be able to create confidence on the markets for anybody to believe in the Scottish pound (we seem to have been able to do that with the sterling £ somehow, despite all our debt!). I suspect they would either have to do a deal with Osborne – who would acquiesce because he will be frightened of the prospects for the sterling £ otherwise. Or they could join the euro – plenty of other countries with hopelessly inadequate financial systems have already done so.
I think there's a load of scaremongering going on here by politicians who may be forced to face up to a complete administrative reorganisation and really would rather carry on as they are with a docile public who don't know/don't care what happens as long as they continue to get their benefits. Of course, Salmond and Farage have put the cat amongst the pigeons here.
There's nothing quite like the Establishment in a panic.