Jefferies analysts on Monday resurfaced an old economic theory that an impending wave of baby boomer retirements could trigger a unified move to liquidate equity holdings.

Such a mass exodus, so the theory goes, could entrench the stock market in a "dark period" for years until younger generations save enough to start repurchasing the assets their grandparents sold.

But Jefferies Global Equity Strategist Sean Darby said that the generational shift doesn't necessarily mean stocks are set for a decade of lackluster performance because foreign investors will fill the void.

"One of the main reasons that investors should not be gloomy about forced selling of retirement plans is that foreign ownership of the US equity market is climbing," Darby wrote in a note to clients on Tuesday. "The growth of assets under Sovereign Wealth Funds has caused a marked shift towards global equities as capital controls have been relaxed."

What's more, it's not certain boomers will sell stocks and get more conservative with retirees living longer than ever. But there's no denying the boomers will be market force, it's just not certain how they will impact the markets. Right now, workers over the age of 55 years represent a near-record 24% of all U.S. employees, according to the BLS.

One such study on the theory that has raised alarm— and the one cited by Darby — comes from Federal Reserve Bank of San Francisco in 2011, which found evidence that U.S. equity values are tied to the age distribution of the population. Such a relationship, the paper concluded, implies that prices could slump until 2025 until millennials start buying back the stocks their parents and grandparents ditched.