Most of the people who are stuck are folks who either have second mortgages or refi-loans which included a recourse. In order to step away from that you'd have to file personal bankruptcy and that can be really hard.
That being said, I don't doubt for a minute that for the right candidate Google or Facebook would pay the difference on what you owed vs what you sold for if you agreed to pay them back if you left in under 3 years. They aren't stupid and the math works in their favor. ($150K is equivalent to 300 shares of 'restricted stock' @ $500/shr price (they call them GSUs) which vest over 4 years) Top engineers should be getting better than that so its worth a shot.
That being said, I don't doubt for a minute that for the right candidate Google or Facebook would pay the difference on what you owed vs what you sold for if you agreed to pay them back if you left in under 3 years. They aren't stupid and the math works in their favor. ($150K is equivalent to 300 shares of 'restricted stock' @ $500/shr price (they call them GSUs) which vest over 4 years) Top engineers should be getting better than that so its worth a shot.