Exactly how I said it would happen. No more American money? Where are they going to get funding? You realize the U.S. essentially created the Islamic State to overthrow Assad, right? And the idiots dedicating their lives to this have plenty of motivation. If we stop killing over there in lands we don't belong, you stop their recruiting pipeline.
Now Israel is also supporting the Islamic State because they are Sunni and Assad is Shi'a, and Israel is more concerned with how powerful Iran has become as a result of America's brilliant adventures in Iraq. But, again, if they want to destabilize the region that is on them. There is no reason we should be involved.
You are going to have to provide some facts to back this assertion. As I understand it this is the opposite of how it happened. Assad has been propping up ISIS with money arms and oil since day one to create a bigger threat to middle east stability than Syrias own civil war. US is obligated to oppose terrorism and try and maintain stability- so Assad makes sure there is a growing terrorist threat- which makes it really easy for the US to not focus on Syria which is politically super messy for the US.