Assad won’t hurt him. They’re in an alliance for now. It’s all going to be a fight to the last man standing. I posted here an article from NYT. After FSA is done, then Assad might fight ISIS.
I can see Assad turning on ISIS once the FSA is finished - at that point he really won’t need them anymore and they pose a potential long-term threat to his regime’s survival.
Here’s the article about Abu Bakr al-Baghdadi hotfooting it back to Syria, by the way.
http://www.aawsat.net/2014/08/article55335468