RIP to the dead.
The thing is, if not ISIS it will be other groups. The whole world has to work towards realising that we can't afford to sleep anymore like during the rise of Nazism. The ideology.. the extremely intolerant, illiterate, barbaric, medieval and fascist subhuman religious ideology that has come to prominence needs to be fought at every level.
Also, no sticking your head in the sand or thinking that this is good/that is bad will work. A massive purge needs to happen all over the world. Muslim and Non-muslim countries alike. Zero tolerance towards anything that is against humanity and promotes crappy unscientific backward thinking. By any means necessary.. It's high time now..