I don't think they really have backpack nukes. The calling card of Islam is that their violence is limited only by their capability. If they had nukes, we'd know in very short order.
The likelihood that any Soviet-era nuke is a) in Islamic hands, and b) is still operable, is next to nil.
Why, because Arabs are stupid and break everything? Pakistan built their own nukes and called it "The Islamic Bomb". Somehow I don't think the "Islamic bomb" is 25 pounds of uranium and a jihadi with a sledgehammer.
Underestimate your enemy and pay high tuition fees on retraining.