I think the hope of us who tend to a more localized US focus is that without the US as an ever present factor, the Sunnis and the Shiites will return to their prime concern of countering each other. And with a lessened US involvement, Israel and the Saudis might act on their common interests and common danger to produce a more durable regional stability.
Another thing I get tired of hearing is how every new tinpot dictator that comes down the pike is “another Hitler” and that our failure to overthrow him and occupy his country is “another Munich.” My response is: When Iran’s Rouhani or Syria’s Assad controls all of one continent and good sized chunks of neighboring continents, let me know. Otherwise, it all sounds like a hysterical little kid throwing a hissy fit.