Risk-free interest? In a bank? Are you kidding?
If you pick a large bank, your deposit is within the limit for federal insurance, I guess you could say it is risk-free.
The insurer has the ability to print money as needed and if needed, so this question makes no sense in respect to him. In short, bank debts will be socialized. But I was actually asking about risk-free interest paid on bitcoin deposits, if there would be such. So no FDIC and no printing press at Fed that would help a failed bank's depositor out.