You're way out of date. That's the way it was before the new bankruptcy laws. but it's a new game in town now and that playbook won't work anymore.
A mortgage holder's recourse in the event of default is the repossession of his collateral. You don't need protection from your creditors if you fully intend to allow them to exercise their legal rights to their collateral. You just give the bank the house and walk away. That is all they can get for the mortgage. If the price has fallen 20%, their problem, they eat the loss.