As ISIS are more about Iraq than Syria, would the increased power vacuum of a bombed Assad of just allowed them to go further?
Not sure about your assertion about the Iraq and Syria difference. Whilst originating from Iraq, it was the conflict in Syria that allowed the pre-ISIS fighters to regroup and flourish (after being practically wiped out by SF operations in Iraq) in Syria's eastern ungoverned provinces. I suppose they have captured much of their materiel from the Iraqi Army though and are supported by former Baathists so can see that side of your point.
As to the question, who knows! As I mentioned, the bombing wasn't designed to be an intervention or remove Assad but no idea if it may have gone the way of Libya; I did express my own personal view in the previous post though. Interestingly, Raqqa fell to the rebels in Aug 13; the same month as the 'no' vote. It fell to the FSA and Al-Nusra and it wasn't until later did ISIS push both groups out of the area. Could the war have been ended before ISIS grew in strength? I don't think so as it was well in full swing with different actors involved but we may have seen less radicalisation of parts of the Syrian Sunni population resulting in groups like ISIS being weaker. One thing is certain; it would have remained an absolute cluster!