Given that the European Central Bank doesn't act as a lender of last resort for individual banks (and really doesn't like being for the Eurozone, cf Greece) it isn't going to step in to cover Scotland. So you're either looking at another Government or perhaps one of the massive re-insurers, can you imagine what the insurance premiums would be on that arrangement?

The much more likely alternative is that the Bank of Scotland and Royal Bank move their HQ to London. Standard Life (and therefore Aberdeen Asset Management) probably as well. Not all their staff will move, but their profits will and some highly paid staff will go. That will in turn have an impact on the nascent FinTech sector.