The most hard-core fighters, those closest to ISIS leader al Baghdadi are apt to join clandestine groups in Syria and Iraq, such as Fateh al-Sham, and Ahrar al-Sham where they will rest, recuperate re-arm and try again, most likely in ungoverned areas of Iraq and Syria. Some may join al Qaida, but that could take time, as the rift between them is very deep. They are likely to seek out ungoverned areas still beyond the writ of either Syrian or Iraqi government forces and their allies.

A second group will be the "free agents" aka mercenaries who cannot return to their home countries:

A second group of fighters are those potential “free agents” or mercenaries who are prevented from returning to their home countries. They can be expected to form a cohort of stateless jihadists who will travel abroad in search of the the next jihadi theater—Yemen, Libya, West Africa, or Afghanistan—to protect, sustain, and expand the boundaries of the so-called caliphate. These are the militant progeny of the original mujahideen, or transnational jihadists that once filled the ranks of al-Qaeda and fought in Afghanistan against the Soviets, and in Chechnya and the Balkans. ISIS affiliates and local Sunni jihadists in these places would likely welcome an influx of battle-hardened comrades.

Behind door number three will be the third group referred to as "the returnees". They will cause counter-terrorism experts the most concern:

These fighters may attempt to return to their countries of origin, like Tunisia or Saudi Arabia, or go further afield to Europe, Asia, or N