In the US, your Promissory Note and State's laws will likely determine the outcome. You have to read the fine print of your loans and look at the state's deficiency judgement laws.
If you have a "recourse" note, the bank can come after you for the difference.
For example, most mortgages in Florida are "recourse". First, the bank has to file a foreclosure lawsuit. That can take as little as 4 months to get through the system, but can sometimes take over a year (depends on how fast the courts are moving in your area). The property either goes back to the bank or is sold to a third party at the courthouse. If the bank is shorted funds (whether the first or second mortgage), the bank then files a "deficiency judgement" lawsuit against you personally. In Florida, the banks have five years from the date of the foreclosure sale in which to get a deficiency judgement. Then, the bank has 20 years to go against you personally. They can garnish your paycheck, levy on bank accounts, get personal assets, bank accounts, and other property you own. Even if you do a short sale, the bank can do the deficiency judgment route. One of the greatest ways to get out of the deficiency judgement route is to make the bank sign a release.
Banks are generally not pursuing this route at the moment, but I think as soon as they (or their attorneys) dig out of the foreclosure mess, they will get the deficiency judgments. Then, they will be able to sell the deficiency judgement to collection companies for pennies on the dollar.
It is my understanding that California mortgages are generaly "nonrecourse". Meaning, that the bank can only come after the mortgaged property.
In short, anyone on this board who is facing foreclosure NEEDS to get an attorney. There are many ways to fight this, and a good attorney can do it for you.