There's no world in which economic growth is low enough that 30 year bonds win out over equities, yet high enough that the US can afford to pay their debts in full without inflating them away. Economic growth isn't a given, sure, but there basically isn't a plan that works for that pessimistic of market conditions. If there isn't enough economic activity to support retiring a large majority of your generational cohort, then unless you save extraordinarily large amounts of money you simply don't get to retire.