Scotland could certainly use the pound (like how Cuba and Zimbabwe use USD), but England (and Wales) wouldn't like it and might move to make it difficult for them if they so wish.

If Scotland votes to leave it will be to remain in the EU debate after Indyref1 led me to conclude that Scotland would have to petition the EU to join as a new member instead of inheriting the UK's membership, and the EU requires new members to adopt the Euro... so if Indyref2 passes then they'll have the Euro.