I could be wrong, but if Scotland does leave the UK, it cannot keep the pound if it wishes to join the EU. They could if they remain independent, but if they go to join the EU, they would not be allowed to keep the pound as currency and would have to take the Euro.
I admit I am not up on all the particulars, but at first blush, this doesn’t seem all that well thought out.
I’ve read opposing claims about the necessity of Scotland adopting the Euro if it joins the EU, and I don’t know which to believe. In any case, as the EU just said, Scotland would have to reapply as an independent country for EU membership; it doesn’t simply convey from its prior association with the UK.