This just keeps getting worse. Because IS achieves victories, Islamic fanatics from all over the world flock to them, which strengthens them, letting them achieve more victories... That's a rather difficult situation to stop. I'm afraid this might have gone too far, they're essentially a separate country now. A country that keeps expanding. They have jet fighters, armor and a large enough military to count as more than a terrorist group. They might have already crossed a point when just killing them will be able to uproot them. Of course, you could just burn down/execute the whole state, but genocide is generally frowned upon these days (though given everything, I'd support such a thing, should it happen).
The scary thing about IS is that they actually seem to push towards establishing a functioning Caliphate, instead of just trying to terrorize everyone. They're calling for skilled technicians and doctors, meaning that they do have a plan to establish a functioning state. They are not a gathering of religion-crazed madmen, at least not anymore. If this continues, I'm afraid that we are going to have a large Arab state on our hands, united by a despotic, violent and highly anti-Western (but disturbingly stable, and likely very well armed) theocracy. The very existence of both Iraq and Syria might soon be threatened (or already is).
Islamic State needs to be destroyed. At this point, I'm personally willing to accept witch hunts, genocide, or even nuclear weapons. Something needs to be done, and we're running out of something that would help. They are targeting the entire non-Sunni world (yes, that means Shia and other Muslim denominations aren't safe, either) and every Sunni area that they don't control already. My only hope is that the next attack happens in Russia and kills someone important enough to piss off Putin and the Russian oligarchs. Indeed, I'd gladly see the entire IS relocated to Siberia and worked to death in Gulags. If anyone deserves this fate, it's them (and yes, forced prisoner labor is still a thing in Russia). Given how they run thing, they might be too smart for that, though...