Mass extermination is not likely to solve the problems of terrorism and the rising threat of terrorist organizations such as the ISIS. This is because Islamic terrorism is based on an ideology rather than on individual people. And for as long as the ideology of terrorism lives on, new terrorist organization will keep on springing out from within the existing organizations from time to time in their fight for establishing a ruthless Islamic state.
Hence, mass extermination might solve the problem for a short term but it is not a long-term solution and can make things even worse due to the causalities that the innocents will suffer from.