The most desirable outcome for all (starting with the Iranian people) would be a regime change. An attack on Iran would probably strengthen the regime by making Iranians instinctively rally behind their government. But that government shows no signs of softening its hard line stance. The opposition sat out the most recent election because they perceived (probably correctly) that the results were a foregone conclusion, and the regime threatened them not to contest the (foregone) results. Plus, the regime does not hesitate to brutally suppress dissent of any kind. So, the "winners" were Khamani and Ahmadinejan, the same two who have no incentive whatsoever to abandon their nuclear ambitions and their dictatorship.