If Scotland does leave, which I doubt it will do, then it will probably be in everyones interest for Scotland to have a currency that is linked to Sterling.
For political reasons, the Chancellor is saying it won't happen, but the BOE will convince him, or his successor that we shouldn't cut off our noses to spite our face. Ireland retained sterling when it went independent, so it is not exactly new territory.
Likewise the EU. They are claiming, again for political reasons, that an Independent Scotland will not be able to join, but if we get to the point where Scotland is independent, the EU will be begging them to join.