Group Health Cooperative is reorganizing in the midst of grim financial results, with the resignation of its chief financial officer and a notice to employees that job cuts are down the road. The Seattle-based health system needs to cut annual expenses by $250 million by the end of 2013, CEO Scott Armstrong said in an email to employees. Richard Magnuson, executive vice president and chief financial and administrative officer, is leaving in the next few weeks. Group Health officials said Magnuson's resignation was prompted by a larger reorganization already in motion.