Equally important, Cohen said, Bank of America Merrill Lynch views the Berkshire move “as an indication of the attractiveness of the surplus lines business.”

He said that Lexington, AIG's main surplus lines vehicle, contributes 12.4 percent of AIG's total P&C premiums and 18 percent of AIG's statutory U.S. P&C direct premium written.

Those leaving AIG to join Berkshire Hathaway were Peter Eastwood, the head of AIG's U.S. property-casualty operations; David Bresnahan, president of AIG's Lexington unit; Sanjay Godhwani, president for Latin America and the Caribbean for AIG's property-casualty operations; and David Fields, another top property-casualty executive.

UPDATE: AIG Names Head of Lexington; Completes Transition After Berkshire Departures

In order to deal with the departures, AIG over the weekend recalled Robert Schimek from London to become president and CEO of AIG Property Casualty's Americas region.

It also named Alexander Baugh to assume responsibility for AIG's global casualty business. He will report to John Doyle, CEO of Global Commercial Insurance within AIG Property Casualty.

Nicholas Walsh, who ran AIG's international property casualty businesses for many years, will become president and CEO of AIG's Europe, Middle East, and Africa region, succeeding Schimek on an interim basis as the company seeks a permanent successor. Walsh is currently vice-chairman of AIG property and casualty in New York. He will be moving to London on an interim basis, company officials said.

Paul A. Newsome, managing director of insurance research at Sandler O'Neill in Chicago does not think this personnel change will be a critical issue for AIG. “Down the line it represents some competition for their excess and surplus lines, but that is it,” Newsome said. “They have had to deal with a lot of departures for a long time.”

Cohen said in his investor's note that he did not believe the moves signaled anything negative about AIG but was likely prompted by a good opportunity for Eastwood and this team. Cohen said that the move would leave AIG with “several slots to fill,” but that the company has a deep enough talent pool to continue running its business as usual.

In its initial response, Matt Gallagher, a spokesman for AIG, said, “AIG has strong leadership in place. AIG has a seasoned and very deep bench of talented property and casualty executives ready to assume broader responsibilities.”

Gallagher said that, “We have hired a number of strong industry leaders over the past few years, including in commercial underwriting, specialty and aerospace, and our executives have the hard-earned experience of leading our business through unprecedented times and circumstances.

“We continue to look to tomorrow and the opportunities ahead for AIG and our customers,” Gallagher said.

This morning, Peter Hancock, president and CEO of AIG Property Casualty, said in announcing successors to the departed executives that, “Rob, Nic, and Lex represent what is most powerful about AIG: a strong bench of seasoned property casualty experts with deep product and global expertise who work closely and tenaciously to help clients and brokers embrace opportunities and face challenges all over the world.”

Hancock noted that in the last several years, AIG has refocused its business, improved its risk selection and is delivering “outstanding service” to its brokers and customers.

“I have every confidence that our people, through leadership, teamwork, and our knack for finding the answer, no matter how difficult the problem, will continue to win on the merits in every market where we choose to compete,” Hancock said.