If Assad prevails,what are the consequences? For Syria, probably continued ethnic strife, maybe even regional and sectarian fragmentation. This is not unusual: think Yemen today, and perhaps Kabul in a year or two. For Iran and its proxies, a kind of victory. [But is that enough to justify U.S. intervention? Not for me. That would make it even harder for America to preserve a military option for dealing with Iranian nukes.] For the Sunni-led Gulf states, more uncertainty and worry, though that would also happen if a weak and divided rebel force succeeded. For Israel, probably a sense of relief, since it would be dealing with a known but weakened Syrian leadership.
Stewart Patrick of the Council on Foreign Relations suggests that an Assad victory could mark the death of the noble Responsibility to Protect [R2P] policy endorsed by the United Nations. But he also notes the other likely costs of U.S. intervention.
But the strategic, economic, and human consequences of a U.S.-led military intervention in Syria are hard to predict. The costs—for regional instability, budgetary overstretch, and U.S. lives—could be gargantuan. And they need to be weighed against the likelihood (and benefits) of “success”—something the administration has yet to define. This cost-benefit analysis must also include an honest assessment of the expenses associated with “the responsibility to rebuild” the post-intervention society (something the Bush administration notoriously neglected to do in Iraq).It's tragic that more than 93,000 Syrians have died in the fighting in the past two years, and that hundreds of thousands remain in refugee camps with dismal prospects for the future. Those tragedies have to be weighed against the large but unknowable tragedies of western military involvement.