Except I watched a friend struggle and continue working rather than retiring when the Great Recession hit. Her 401Ks tanked.
I think the only solution would be some sort of FDIC type backed pension system.
I think it would be better to have the 401k's, just with maybe a bit more hand-holding - i.e. "retirement target 2040" accounts. People can sign up, and as they get to within a few years of their target date, stocks are gradually shifted towards bonds, or just straight cash. That way you don't have to risk selling when it's just tanked.
The problem with the pension method is that when the economy is bad, we, the taxpayers (who are also probably hurting in the middle of a depression - government tax revenue tends to drop substantially) are still on the hook for the same amount of cash. It just shifts the risk from retired public employees to taxpayers - and so many other services get cut to keep paying out the pensions.