But the point remains, there is precedent for a member of the UK to retain a form of currency union post independence. Ireland didn't leave the pegged Sterling because of the supposed stultifying effects of the Irish Pound being linked to the British Pound, they did so because of policy differences with the UK about the linked currencies and EU fiscal policy. If EMU didn't exist then I'd wager it'd still be the case today.
If anything there's an economic argument for a new nation like Alba having its own currency linked to Sterling being a boon to retaining and attract new industry by having a currency linked to the mighty, safe Pound rather then a potentially tricky new currency (Scottish Lira?).
There is precedent for new EU members to keep their own currency upon entry if they so wish. If a war ravaged and wary Irish Free State can kiss and make up with the British government enough to have linked currencies, then surely 21st Century Scotland and the UK can do likewise? It would be my own opinion that as Scotland has been in full economic union with the rest of Britain for the past three centuries then the Sterling is as much theirs as it is the rest of the UK's.
If, in the highly unlikely event the Scots do vote for independence, I imagine this currency debate will be seen for what it is, politicking, electioneering and fear mongering by the various pro and anti independence groups. Scotland, like Ireland in the 1920s, will still be heavily linked economically with the rest of the UK. A form of currency union between Scotland and the rump UK state is almost inevitable.