If MBIA and AMBAC fail (they are close to insolvency) then all their insured MBS bonds will be derated to junk, unless the originators have the capital to self-insure them (they don't).
If this happens, our financial system could face its worst crisis in 75 years.
I’m assuming the guys who got rich from this mess have their assets safely squirreled away. Like I said, the devil take the hindmost.