I think that as Secretary of Defense Carter said, the head of the snake is in Raqqa, and that is what must be cut off.
To cut it off, Raqqa must be invaded, which is going to be costlier and bloodier than the battle of Fallujah, some years ago. Furthermore, Raqqa is full of civilians. It is a big town.
The way to go about it is to start doing raids at night primarily with stealth helicopters ala Bin Laden raid, and terrorize the ISIS crowd. They know where they are, they just can't bomb them for collateral damage, so raid them, and keep wearing them down, kill their leaders along the way. I also think the europeans should get involvd with special forces, not just us. Turning Raqqa into rubble with bombs is not a solution. It is a war crime, and an unconscionable act.
Otherwise, the head of the snake will still be the beacon inspiring these attacks. The head must go. The Europeans must face the music, at last.