Yes I think its fully possible for ISIS to start a new WW, ISIS is an terrorist orginasation known for killing many and causing widespread fear. Right now, ISIS is getting everyone against them and pulling armies closer to each other. I think ISIS is highly capable of starting and holding up a war, wich is not goos news for anybody.
I just can't see it happening, I wouldn't call it a World War as opposed to something similar to Vietnam, they all live in a desert so unlike vietnam we can just mortar their patrols and weaken morale. I think that the forces in the middle-east are strong enough to stop ISIS eventually themselves. With all these people getting involved, I can probably predict ISIS wont mean anything by 2020's. You have nothing to worry about, no big bad terrorist organization has caused anything more than a minor disturbance yet.