If I could suggest a solution... the UN and all of its members step up with coordinated resources to methodically get rid of them as quickly as reasonably possible.
...
That is the typical generic "solution" and it never works.
What do you want the UN to do?
-Sanctions? Sanctions against who?
-More drone strikes? How is that any more accurate than an unconventional response?
-Throw together a rag-tag guerrilla battalion, arm them to the teeth and watch them hand over their weapons to ISIS?
Nobody has any viable solution. There is no viable solution. There is only a finite solution.
All the talking heads do is criticize others for wanting justice. People outside of the situation look down on it as if they are better than those who who want revenge. But they never offer any solutions. They simply have their own self-image agendas in mind.
I look at this situation as if it was a hijacked plane. The plane itself can be used as a weapon, therefore the innocent people on board who are being held hostage are, sadly, doomed no matter what.
If need be, you destroy the plane over open land to prevent the hijackers from using it to kill anyone else. Yes, the innocent people on board would be killed. But nobody else would be killed. That was an option the military had on the table during 9/11.
Those poor people on board are doomed because it's impossible to save them without conceding to the terrorists.
It was up to the passengers to force the hands of their captors. We saw during 9/11 when the people on that one flight tried to storm the cockpit - the terrorists intentionally crashed the plane short of their destination because their hand was forced and those brave people on board did not want to die with their hands simply folded on their laps.
In this situation, ISIS can't have their hands forced. They simply kill anyone in their way outright or make propaganda out of their executions. They people they invade are unarmed and largely defenseless. And their hostages are reporters who simply report news.
I know it's hard to understand this for some people, but the people being held captive by ISIS are not in the situation where they can force anyone's hand. So, they are largely doomed no matter what.