If ISIS takes over Iraq, it will be a catastrophe. Remember the morale and prestige boost the Mujahadeen got out of chasing the Soviets from Afghanistan?
If ISIS can make the claim that it collapsed the US-installed regime in Baghdad, followed by the collapse of Aghanistan in a couple of years (if not sooner), the Salafist gain will be incalculable.
At least, though, the USofA will not collapse in the aftermath like the USSR fell apart after being chased out of Afghanistan.
Don’t leave out Libya and Syria.