State residents insured by Blue Cross Blue Shield of Massachusetts have started receiving refunds stemming from the health plan's decision to distribute a total of about $4.2 million to its members, an amount equivalent to the severance paid to its former chief executive, Cleve L. Killingsworth. But if policyholders expected to be taking a vacation with the money saved from their "premium credits," they may want to set their sights on a latte, instead. "You will see this one-time credit of approximately $3 per policy on the enclosed invoice,'' Blue Cross, the state's largest health insurer, wrote in notes sent with premium invoices this month to about 38,000 individual policyholders. Blue Cross disclosed in July that it would issue the refunds to close the books on its widely criticized $11 million exit package for Killingsworth, who resigned abruptly last year. The decision to refund the severance pay portion came after talks with Attorney General Martha Coakley's office, which conducted a four-month investigation. The office concluded that while Killingsworth was entitled to the money under his contract, the generous severance did not serve the purposes of a nonprofit insurer.