Had he walked away from the property, he’d still have his 401k (protected from creditors by federal law; he could’ve lived in the house for years while it went through foreclosure and put his mortgage payments in his 401k) and if the lender absolutely decided to pursue the deficiency judgment (rare), he could’ve settled for pennies on the dollar or declared bankruptcy and still been hundreds of thousands of dollars ahead.
Just sad. My advice to those who read this: never get emotionally invested. It’s just business. Look at the numbers, and throw out any sense of morality of the debt repayment. That is how the system is built; act like a rational actor within it (losses are built into the mortgage interest rate). Your future self will thank you.