Shares of Yahoo tumbled Monday after Chief Executive Jerry Yang fended off Microsoft’s three-month courtship of the company he co-founded.

In the aftermath, investors, employees and executives were left to consider an uncertain aftermath.

A research report from a team of UBS analysts concluded that:

    Google had triumphed because “its most threatening competitor,” Microsoft, had failed to achieve the scale it sought.

    Microsoft still needs Yahoo to compete against Google and could revisit the deal barring a serious search alliance between Google and Yahoo.

    Yahoo will face shareholder lawsuits and will have to drive initiatives to push up its stock price to placate skeptical investors.

    AOL hypothetically could become a smaller-scale merger partner for Microsoft, but the struggles of the Time Warner unit make any such deal in the near term unlikely.

In a letter to employees after Microsoft withdrew its offer, Mr. Yang sought to rally the troops, acknowledging that Yahoo would remain in the spotlight and revealing that he and Chief Financial Officer Susan Decker plan to tour company offices as the company refocuses on growth strategies.

In late morning trading on the Nasdaq, shares of Yahoo fell $4.14, or 14.4 percent, to $24.53, well above the $19.18 close before Microsoft announced its $44.6 billion stock and cash offer on February 1.

Fred Wilson, a blogger and venture capitalist at New York’s Union Square Ventures, polled readers on the likely closing price of Yahoo at the end of the trading day Monday. Their conclusion: $22.

Microsoft’s offer initially was valued at $31 per Yahoo share, but Microsoft Chief Executive Steve Ballmer raised the offer to $33 per share. Yahoo, however was holding out for about $37 per share.

In a letter to Mr. Yang, Mr. Ballmer said Microsoft decided not to stage a proxy fight because Yahoo had threatened, during the hostilities, to conclude an alliance with Google to outsource search advertising that would have made Yahoo an “undesirable” acquisition.

Such a move, Mr. Ballmer wrote, “would fundamentally undermine Yahoo’s own strategy and long-term viability” by sending advertisers to Google instead of Yahoo’s own Panama search system.

Though Microsoft could return to its previous strategy of growing its online business through partnerships and small acquisitions, the UBS analysts said such a “go-it-alone” program would allow Google to extend its lead.

Alternatively, Microsoft could borrow the strategy Oracle used in its successful hunt for BEA Systems by coming back to the deal at a later date. “We believe that the door is still open for a Microsoft and Yahoo tie-up barring any interference from Google,” the report said.