Bill Gross, co-chief investment officer of Pacific Investment Management Co. (PIMCO), left, looks on as Laurence “Larry” D. Fink, chairman, chief executive officer and co-founder of BlackRock Inc. Gross, co-founder and chief investment officer of Pacific Investment Management Co. will join Janus Capital Group Inc. Photographer: Andrew Harrer/Bloomberg.

Fund research firm Morningstar stripped Pimco’s flagship Total Return bond fund of its gold rating Monday night, citing uncertainty over outflows after the departure of co-founder Bill Gross.

Investors yanked more than $10 billion from Pimco after it was announced that Gross was leaving the firm, the Wall Street Journal reported Monday. Those outflows could be just the beginning, with Morningstar predicting that “likely tens of billions, if not hundreds of billions” in assets will follow Gross out the door to Janus Capital, where he will manage a new unconstrained bond fund.  An analyst for Citi estimated the potential outflows could amount to $400 billion, or 20 percent of the Pimco’s $2 trillion in assets.

“Given Bill Gross’ abrupt departure, investors have focused on the possibility that outflows could wreak havoc on the portfolio,” Eric Jacobson, senior analyst at Morningstar, said in the report explaining the downgrade .

With so much money leaving the firm, do investors have any reason to stay?

It depends on why they invested in Pimco in the first place. Many people who bought Pimco funds because they believe in Gross will likely follow him to Janus, analysts and financial advisers say.

“The mystique is gone, and now you’re just with Pimco,” says Rick Ferri,  founder of Portfolio Solutions, an investment management firm in Troy, Mich. “And not that that’s bad or good, but maybe there are other places to go that are less expensive.”

Some of the cash leaving Pimco will head to competitors offering large bond funds. Some people may see this as a chance to switch from active management to a less expensive index fund, Ferri says. For instance, the $120 billion Vanguard Total Bond Market Index fund, which also tracks the Barclays Aggregate Bond index, charges 0.20 percent, or $20 for every $10,000 invested. That compares to the 0.85 percent expense ratio on the Pimco Total Return Bond fund, or $85 for every $10,000 invested. (Meanwhile the Vanguard fund has gained 3.9 percent in the 12 months ending Friday, compared to a gain of 3.1 percent for the Pimco fund, according to Morningstar.)

People who stay with Pimco may need to be patient with the firm as it stabilizes following the departure of its top two leaders. (Former chief executive Mohamed El-Erian left earlier this year.) Jacobson of Morningstar said it will take time to see how the new managers will perform but added that “there are a number of reasons to believe they will be successful after the dust settles.” The new chief investment officer is Daniel Ivascyn, 45, who was named Morningstar Fixed-Income Fund Manager of the Year in 2013.

“We have assembled a team of world-class investors over the course of many years, and established a time-tested top-down, bottom-up investment process that will guide our investment philosophy and continue to serve our clients well into the future,” Ivascyn said in a statement.

Because roughly half of the fund is in short-term bonds, which investors can buy and sell easily, managers shouldn’t have a hard time selling bonds to pay what is owed to investors leaving the fund, says Russel Kinnel, director of manager research for Morningstar,  That should help to stabilize performance, even as investors take their money and go. “Ten billion isn’t a problem for a giant fund in the $200 billion range,” he says.

And some of the people who invested in Pimco’s flagship fund for its strong returns may already have been on their way out. Last May, long before Gross announced his exit, investors staged an exodus. After 16 months, they’ve pulled close to $70 billion from the fund.