They should have this option
What is preventing nations around the world from using american dollars, euros, or various other currencies from around the world? Any currency should be acceptable in any country, as long as there is currency exchange available.
Are people really so silly as to prevent other nations from using their currency? That makes your currency more valuable; the more people who accept it, the more it buys! It's the whole point of the U.S. attempting throughout the years to get the dollar as the currency everyone relies on, and why, guess what, the pound sterling was the international currency before the U.S. dollar. Now, why they would choose to keep the pound sterling over a different currency, well, that's for the Scots to decide.
Absolutely not! If they vote for independence, that is exactly what they get. The Euro is a prime example of why a shared currency can be disastrous and to risk a Greece-like situation would be most foolish. If Scotland did fail economically it could make the entirety of the United Kingdom suffer and this is in no way right. Independence has risks, and they should take them, not England, Wales and Northern Ireland as well.
Independence is as independence does.