Legal Question in Real Estate Law in California

A short sale is a privately-negotiated deal between "consenting adults" - the buyer, the seller and the lender. The seller's being in default is usually a major factor in the lender's interest in permitting a sale to take place that results in a short pay-off. Most major banks seem not to even discuss a short sale until the borrower/prospective short seller has stopped making payments. Still, I know of no absolute rule or law that would prevent a bank and a non-defaulting borrower from working out a compromise pay-off when the bank saw an advantage in doing so. A case in point might be a property with a serious environmental problem and clean-up exposure where the bank saw an opportunity to avoid future remediation responsibility.