The Nexerus said
Hypothetically, Scots would still be able to use the pounds in their wallets to go the store and buy groceries, but the Bank of England absolutely can and absolutely will disavow an independent Scotland from using the pound sterling without an adequate negotiation process. If you want Scotland to be like Zimbabwe and have no currency on a government level and use a foreign currency on the level of actual citizens, that's fine, but if not, Scotland needs to negotiate the terms of a currency union with the Bank of England, and accept that they're negotiating because it is the Bank of England and the Bank of England alone that dictates the pound.
The entirety of the argument is on the Bank of England bailing out Scotland on the basis of economic collapse, the same way that the US national reserve bails out various countries as a whole, as it's the international reserve currency. That's all their disavowing has powers to do, unless the sterling becomes the national reserve currency, it cannot actually effect trade.
But, again - if a huge chunk of your union was leaving without any change, and they were offering to pay for a proportional level of the debt, and that they're already your 2nd highest trading partner in the world, would you actually think it's a bad thing? I mean, put it this way - as the bank of england, there wouldn't be any more difference as it would be if scotland was simply a fully devolved country within the union.
And, as you said, the Euro is there.
If I got to name a new currency, i'd call it the #YOLO