I don’t see your concern
ISIS or any other Radical Islamic entitiy may not turn off the spigot, but they will selectively sell crude to non-west interests. The immediate effect would be a disastrous whammy on the European economy, starting with bond defaults. This in turn , as you know would domino into a world wide financial crisis. Even if we build the XL pipeline, a crumbling european economy will domino over here, and eventually world wide.
If it looked like some force would take over Saudi Arabia, Europeans could step in to defend the Saudis or Saudi Arabia could buy what it needs to protect itself. Europe can get their contracts for oil elsewhere, perhaps from us, and the oil from Saudi Arabia is sold to Russia or China or whatever.
It’s all the same basic commodity and even if the Saudis are taken out, we have plenty here now that we never knew before.
I don’t see the problem, still.