You can't blame Cleve Killingsworth, not entirely, for pocketing his absolutely obscene $4.2 million severance package from Blue Cross Blue Shield of Massachusetts, the giant insurance company that he left last year under circumstances that remain unexplained. But there was a glimmer of justice in Attorney General Martha Coakley's announcement last week that an amount equal to that hefty sum will be returned to Blue Cross customers. Killingsworth keeps his money, but the customers are no longer left with the tab. Blue Cross customers are not going to see a windfall from this agreement; it works out to about $1.50 per customer, on average. But Coakley said it sends a message of restraint.