They think Armageddon will bail them out on the mortgage so they won't have to pay it off, but in reality they will simply die in debt -- but at least they won't have to pay it off.
Hopefully they are a childless couple. Not that you should rely on your parents passing anything on to you, but to have them live in a financially reckless way due to an outside influence that they chose to follow without thinking is likely disheartening and something many only discover after their parents pass away. Or worse, will become a burden to their children in later life.
For any boomer to die in debt represents a massive failure in good life choices, because they really were handed a favourable system (to them) on a plate.