Um, not according to the Goldman Sachs report that flew across my desk few days ago. Banks are not carrying their debt on their balance sheets marked at 50. None of them.
Banks could still sell their toxics assets at 50 like you describe, but they won't. That would require them to take huge write-downs that they're not willing to suffer. They'll just sit on it instead - or buy their own debt and stiff the taxpayer throught the FDIC's non-recourse loan.