Yeager, I think this will follow a typical escalating path.
My personal presumption would be that the the terrs won't resort to nukes unless the world-wide (I hope) coalition of "good guys" begins to get the upper hand. If the terrs get into a desperate situation, where they are cornered, with no sanctuary and and the "law" closing in... then they might use the weapon that will earn them eternal damnation in the eyes of the world regardless of any political considerations.
Further, I don't expect the "good guys" to really get a handle on this problem for decades... and that's how I came to my hypothesis.