Like WillPostForFood, I'm baffled about where you're even getting this idea.
The 401k is their money. Right now they could withdraw all the money. If their employer goes bankrupt, the 401k balance didn't change at all. The only part that could potentially go away would be unvested company contributions (I'm not sure on this - it's all I can think of though).
If we were talking about a pension, Social Security, or a 457b deferred compensation plan - I get it. There's uncertainty. Pensions get underfunded routinely, private equity shenanigans occur etc. Social Security will likely see big changes in the next 40 years. In the case of the 457b plans, it's not your money until you leave the employer and start withdrawing money.
Please clarify your statement if you have something productive to add.