Here is the answer to my own question
In summary: it depends on the state and your loan.
if you live in CA, and if your loan is for the purchase amount, then even if you walk away and the house value is a lot *lower* than the foreclosure sales price, the bank will not run after you.
(The will though if you refinanced with a higher loan than the initial purchase price, or in some states)
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*Deficiency judgment*
*Legal action sought by a lender who wants to recover any losses on a foreclosure*
If you default on a mortgage, the lender can not only sell your property to get their money back, but they can also sue you if the money from the sale isn’t enough to cover the loan. For example, if you owe a lender $100,000, but the lender only gets $90,000 in a foreclosure sale, they can take you to court for the remaining $10,000. If the lender wins, they can attack your assets, income, credit and peace of mind until you pay this amount. If you have Private mortgage insurance, a lender can use this money to offset any losses instead of getting a deficiency judgment. Keep in mind that only some states give the lender the right to a deficiency judgment.
However, a lender cannot obtain a deficiency judgment if the underlying debt arises from "purchase-price loan," which is either a "seller carry-back loan" (see above) or a third-party purchase price loan for a owner-occupied residential property that has no more than four units (see above).
The matter can be summarized as follows. A lender cannot get a deficiency judgment if it forecloses by private sale, nor can it do so if the underlying loan was a purchase-price loan. Therefore, a lender will choose to sell the property at a private sale if (1) the sales proceeds will pay the entire loan or (2) the loan was a purchase-price loan. Since most loans fall into one or both of these categories, a private sale is usually the preferred method of foreclosure.
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A deficiency judgment is the result of a judicial foreclosure, the process by which a lender takes you, the borrower, to court in an attempt to receive a judgment for the amount that they claim you owe them above and beyond the principal and interest you owe on your loan.
The lender has 90 days to start the motion for a deficiency judgement after a foreclosure sale and the market value of the property must be determined by the court.
In most cases, lenders do not pursue homeowners who have lost their homes to foreclosure and thereby incur a deficiency judgment. Although they may receive a 1099 income statement, lenders realize that they average person who looses their home to foreclosure, most likely will not have the funds to make due on a deficency judgment
In certain states, most notably California, homeowners may not be liable for any deficiency on their mortgage, provided that the mortgage you have on your home is the original one you took out when you purchased the home. This "purchase money" security interest provision means that under California law, you are not entitled to pay deficiencies on your mortgage unless you have refinanced the mortgage since you bought the home. 2nd mortgages which were taken out at the same time as the "purchase money" or original mortgage may also be covered by this provision, however you must consult a legal professional for advice pertaining to your own situation.
In most states, the lender will not pursue obtaining a judgment to cure deficiencies unless the amount owed as a deficiency is very substantial. This is due primarily o the high cost of working through the courts ina judicial foreclosure. Most lenders prefer a non-judicial foreclosure.