There is no sense in moving an entire headquarters just because the country has declared independence. It would waste way to much money to do the move and there is likely to be no true benefit to moving. There are plenty of banks that are operating in a different country.
Scottish banks should stay in Scotland if they intend to be involved in the Scottish economy. Devolution should not cause movement of headquarters unless a bank plans to stop doing business in Scotland. Independence itself as a root cause of movement doesn't make any sense. Banks should, and will, do what they always do -- what is best for the bank.
Scotlan's banks should remain in Scotland no matter what the vote. This is because if such a vote goes through, then Scotland will need all the stability it can get. We do not need a small-scale Euro-zone economic crisis. Even small changes can have detrimental results. The banks are key in this.
If Scotland's banks move their headquarters to England, why call themselves Scotland's bank? That would be as if the Royal Bank of England decided to relocate to Miami. The entire proposition is entirely absurd. The banks and the people of Scotland are simply going to have to grit their teeth and get through the inevitable post-independence financial collapse.