If Congress passes ObamaCare, should retirees be on guard? Not necessarily, says Susan Berson, senior health care industry attorney at the Washington, D.C., law firm Mintz Levin and former general counsel for senior markets at insurer UnitedHealth Group (UNH). Most of Medicare, the government health insurance plan for those 65 and older, won't change, Berson says. She spoke with IBD about the medical system as it pertains to seniors. IBD: Let's