I don't understand what there is to debate here. If they leave, we both have a currency called the pound. Ours the British pound, theirs the Scottish pound. And it's up to us individually to look after our currency. Of course we don't share a currency.
And it's not us keeping the pound, and them not getting it. We both get our own currency, which starts life in the same place as our current pound. Isn't that quite simple?
Your kinda just offering a name to their 'new' currency, you would still require two printing presses